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Abstract Introduction Methods Geologic mapping is a primary function of the AZGS, so in cooperation with Arizona Department of Water Resources (ADWR) staff we have established procedures and protocols for documenting and mapping the extent of Holocene floodplain alluvium along rivers in Arizona. These practices were first conducted along the entire length of the San Pedro River, Babocomari River, and Aravaipa Creek (AZGS DM-RM-1). More recent mapping efforts have resulted in new and updated surficial geologic mapping covering over 370 river miles depicted in 2-mile-wide strip maps centered on the Verde River and each major tributary. The maps and reports (AZGS DM-RM-2, DM-RM-3) describe river and tributary deposits of Holocene to late Pliocene age, Pliocene and older basin filling deposits, and various bedrock units along the river at a scale of 1:24,000. Several existing AZGS 7 ½’ quadrangle geologic maps in the Verde Valley were updated and re-released based on this new mapping as well as the availability of higher resolution aerial imagery. The strip maps provide basic information on the geology of the river corridors that may be used in future water rights adjudications and define the physical setting of the river systems. Mapping of River Alluvium Along the Verde River and Major Tributaries, Central Arizona Cook, Joseph P. 1 , Pearthree, Philip A. 1 , House, P. Kyle 2 , Bigio, Erica 3 , Onken, Jill A. 3 , and Youberg, Ann 1 1 Arizona Geological Survey, 2 United States Geological Survey, 3 Department of Geosciences, University of Arizona New mapping widens Holocene alluvium from 600 - 1700 feet depending on interpretation of unit CT2 (AZGS OFR 93-16) Close agreement between old and new mapping results in very minor changes in lateral extent of Holocene alluvium. Mapping strategy: • Compilation of existing geologic mapping in an ArcGIS framework • Re-evaluation and revision of existing mapping using aerial photos and topographic data • New mapping of Holocene river alluvium where no large-scale geologic mapping had been conducted previously • Field-checking of the boundaries of Holocene alluvium in various geologic environments along the river, including systematic collection of GPS field points with observations and ground photos • Depiction of all Holocene river alluvium units on 1:24,000-scale strip maps associated with this report In 2010, the Arizona Geological Survey (AZGS) released a series of 1:24,000-scale geologic strip maps showing the extent of Holocene channel and floodplain deposits along the Verde River and five large tributaries in central Arizona. The primary purpose of this mapping was to contribute to the legal differentiation of river subflow from groundwater in surrounding areas, as Arizona courts have established the lateral extent of Holocene river alluvium as a key component in delineating subflow zones. These maps also define the physical architecture and geomorphic framework of the river systems, depicting river and tributary deposits of Holocene to late Pliocene age, Pliocene and older basin filling deposits, and various bedrock units. We employed standard geomorphic and geologic criteria to differentiate and map river and tributary alluvial deposits of different ages. The degree of clast rounding, lithologic diversity, and landform/terrace slope were used to differentiate river from piedmont alluvium. The through-flowing Verde River developed several million years ago, linking several closed or partially integrated basins. When the Verde River became integrated, it began to downcut along its entire course, and this in turn drove deep incision along all of its major tributaries. The maximum amount of incision has probably occurred along the middle Verde River in Verde Valley, where the river has incised at least 300 m below the former valley floor since the late Pliocene. High standing relict terrace deposits all along the Verde River record former river levels through the Pleistocene. Because the Verde River and its tributaries have incised deeply into both bedrock and less-resistant sedimentary basins, the lateral extent of Holocene river alluvium varies dramatically from less than 30 m to over 1 km across. Within this corridor, we mapped up to 6 Holocene units, including active channels, bedrock-lined active channels, flood channels, and several levels of terraces. The extent of active channels, flood channels and low bars change with virtually every large flood. Young terraces are more stable, and typically are subject to shallow inundation in floods. Dates from archaeological sites and paleoflood studies suggest that nearly all of the Holocene deposits along the river are less than 4 ka. Qy3r Qy4r Qy4r Qy2r Dm Tb Tb Dm Qycr Distribution of Holocene river alluvium in narrow bedrock canyon reach in the upper Verde River near Paulden, AZ. All preserved Holocene river terraces are narrow and bound by tall bedrock walls and onlapping colluvium. W e t B e a v e r C r e e k W e s t C l e a r C r e e k F o s s i l C r e e k E a s t V e r d e R i v e r Coconino Yavapai Gila Maricopa Chino Valley North Clarkdale OFR 95-16 Study area Cottonwood Cornville Page Springs Middle Verde Camp Verde Horner Mountain Horseshoe Dam Bartlett Dam Maverick Mountain Fort McDowell O a k C r e e k Footprint of two mile wide map corridor centered on Verde River and mapped tributaries (AZGS DM-RM-2, and 3). Blue boxes represent previous AZGS mapping, the yellow box represents concurrent AZGS mapping. Compilation of existing USGS bedrock mapping outside AZGS mapped areas was also conducted. Qycr Qy2r Qy4r Distribution of Holocene river alluvium in an unconfined reach in the Fort McDowell Yavapai Nation. Flood channel (Qy4r) terraces are extensive and lightly vegetated. Qy2r terraces are often obscured by agricultural use. Holocene river alluvium is bound by onlapping alluvial deposits and eroded basin fill deposits. Pleistocene river terraces - Qi1r, Qi2r, Qi3r • Clay rich, reddened soil horizons • Obvious CaCO3 accumulation • Planar to moderately rounded • Stand high in the landscape relative to the modern river A Pleistocene Verde River deposit capping basin filling sediments near the Verde/Salt confluence stands 165 feet above the modern channel. Pleistocene cap Verde River Active channels - Qycr • Unconsolidated sand to cobbles • Pool and riffle sequences • Lined by riparian trees and vegetation • Commonly submerged Young river terraces - Qy2r • Higher in landscape than Qy3r terraces • Generally fine grained with gravel lenses • Some soil development, minor soil carbonate accumulation • Typically are presently or were historically plowed and irrigated; many now developed • Usually most laterally extensive terrace Dm Incised Qy2r in upper Verde Floodplain / low terraces - Qy3r • Higher than Qy4r surfaces • Only inundated during more extreme flow • Riparian trees and grasses • Former floodplain and river meanders • Mild soil development Qy3r Qycr Flood channels - Qy4r • Adjacent to Qycr deposits • Inundated under higher flow (seasonal or flood) • No soil development • Unvegetated to lightly vegetated • Often show signs of recent flooding Qycr Qy4r Qyc Qyc Qyc Qyc Qy3 Qy3 Qyaf Qyaf Qyaf Qyaf Qy2 Qy2 Qy2 Qy2 Qi3rb Qi3rb Qi3ra Qi2r Qy4r Qy4r Qy4r Qy4r Qy4r Qy4r Qy4r Qy4r Qy1r Qy2r Qy2r Qy2r Qy2r Qy2r Qy2r Qy2r Qy2r Qy2r Qy2r Qy2r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy2r Qy3r Qy3r Qy3r Qyaf Tvv Tvv Qyc Qyc Qyc Qy3 Qy3 Qy2 Qy2 Qy2 Qy1 Qy1 Qy1 Qys Qys Qys Qys Qys Qi2b Qo Qtc Qi3rb Qi2r Qo3r Qo3r Qo2r Qi1r Qo1r Qi2 Qi2 Tvm Tvl Tvm Tvm Tvm Tvm Qycr Qy1r Qy1r Qy2r Qy2r Qyc Qy2r Qy3r Qy3r Qy3r Qy1r Tvm Qys Qy2r Qi1r Tvm Tvm Qyc Qys Tvm Qi3r Qys Qycr d Qi2r Qi3ra Qy3r Qy2 Qy2r Qycr Tvm Tvm Qy3r Qy3r Tvm Qy3r Qy4r Qy2 Qy3r Qis Qo3r Qy2 Qi1 Qi1 Qy3 Tvv Tvv Qy3 Qyc Qyc Qyc Qyc Qyc Qyc Qyc Qyc Qy3 Qyc Qyc Qyc Qyc Qy3 Qyc Qyc Qyc Qyc Qyc Qy2 Qyc Qy3 Qy3 Qy3 Qy3 Qy3 Qy3 Qyaf Qy3 Qy2 Qy2 Qyaf Qy2 Qy2 Qy3 Qy3 Qyaf Qyaf Qy2 Qy1 Qy2 Qy2 Qy2 Qy2 Qys Qy2 Qys Qy2 Qy2 Qy1 Qys Qys Qys Qi3 Qy2 Qy2 Qy1 Qy1 Qys Qy1 Qo1 Qys Qys Qys Qys Qys Qi1 Qi1 Qi2a Qi1 Qo Qi1 Qy3 Qyc Qyaf Qys Qys Qys Qys Qy2 Qys Qy2 Qys Qy1 Qys Qys Qi3 Qi2b Qi1 Qi1 Qi3 Qi3 Qi1 Qo Qo Qtc Qy3 Qy2 Qy2 Qy2 Qy2 Qy2 Qy2 Qys Qi1 Qi1 Qo2 Qo Qy3 Qyaf Qy2 Qy2 Qy2 Qy1 Qys Qi1 Qi1 Qo Qo Qo Qo Qi3ra Qi2r Qo2 Qo2 Qo2 Qi3rb Qi2r Qi2r Qo3r Qo3r Qo2r Qi1ra Tvg Tvl Qis Qi2 Qi2 Tvm Tvm Qyc d Qo2 Qo1 Qi1 Qo2 Qo2 Qo3r Qi3ra Qo2 Qo2 Qo1 Qi2rb Qi2ra Qi2r Qi2r Qo3r Qtc Qi3rb Qi2r Qi2r Qo3r Qo2r Qo2r Qo3r Qo2r Qi2ra Qo2r Qo3r Qi2r Qi2r Qi2r Qo3r Qo3r Qo3r Qo2r Qi1r Qi1rb Qo2r Qi1r Qi1ra Qi1ra Qi2r Qi2r Qo3r Qo3r Qi1r QTo Tvg Tvg Tvg Tvg Qi1rb Tvg Qis Qis Qi2 Qi2 Qis Qis Qi2 Tvg Tvl Qis Tvm Tvm Tvm Qi3r Tvm Tvm Tvm Tvm Tvm Tvm Tvm Qi3r Tvl Tvm Tvm Qi3r Qi3r Tvm Qi3r Qycr Tvm Tvm Tvm Tvm Qycr Qi2r Qo3r Qo2r QTo Qi2 Tvm Tvm Tvm Tvm Tvm Tvm Tvm Tvm Qy4r Qy4r Qy4r Qy4r Qy4r Qy4r Qy4r Qy3r Qy2r Qy2r Qy3r Qy3r Qy3r Qy1r Qy3r Qy2r Qy3r Qy2r Qy2r Qy2r Qy2r Qy3r Qy2r Qy3r Qy2r Qy4r Qy4r Qy4r Qy4r Qy2r Qy1r Qy2r Qy2r Qy3r Qy4r Qy4r Qy3r Qy3r Qy2r Qy2r Qy1r Qy4r Qy4r Qy4r Qy2r Qy4r HV 700 HV 326 HV 192 HV 195 HV 193 HV 194 HV 426 HV 196 HV 197 HV 199 HV 198 HV 191 HV 177 HV 190 HV 176 HV 175 HV 189 HV 188 HV 174 HV 173 HV 187 HV 172 HV 179 HV 171 HV 178 HV 170 HV 186 HV 185 HV 169 HV 184 HV 183 HV 167 4 18000 4 19000 4 20000 4 21000 4 22000 4 23000 4 24000 4 25000 4 26000 4 27000 4 18000 4 19000 4 20000 4 21000 4 22000 4 23000 4 24000 4 25000 4 26000 4 27000 38 14000 38 15000 38 16000 38 17000 38 18000 38 19000 38 20000 38 21000 38 22000 38 23000 38 24000 38 25000 38 26000 38 27000 38 14000 38 15000 38 16000 38 17000 38 18000 38 19000 38 20000 38 21000 38 22000 38 23000 38 24000 38 25000 38 26000 38 27000 PIMA COCONINO MOHAVE GILA YAVAPAI YUMA PINAL MARICOPA COCHISE LA PAZ GRAHAM APACHE NAVAJO GREENLEE SANTA CRUZ L 0 1 2 0.5 Miles Example of laterally extensive Holocene Verde River deposits in the Verde Valley, central Arizona. The Verde River incising into the relatively erodible Verde Formation (lacustrine, mudstone, limestone, gypsum, and diatomite deposits) has resulted in widespread Holocene deposit preservation. The active channel represents only a small part of the river system with much wider flood channel deposits and extensively preserved young terraces. Tributary deposits grade to similarly aged river terraces and in some places cover them. Lateral topographic constraints are composed of older river deposits, eroded basin fill deposits, or onlapping tributary alluvium. HV 512 HV 511 HV 297 HV 296 HV 510 HV 294 HV 508 HV 507 HV 295 HV 509 HV 506 HV 293 HV 292 HV 505 HV 291 HV 504 HV 290 HV 503 HV 289 HV 502 HV 288 HV 501 HV 286 HV 287 HV 343 HV 720 HV 719 HV 342 HV 718 HV 341 HV 340 HV 717 HV 339 Qy2 Qyc Qy3 Qy3 Qy3 Qy3 Qy3 Qy3 Qy3 Qyaf Qy2 Qy2r Qy2 Qy2 Qls Qi3 Qi1 Qi1 Qi2r Qi2r Qi2r Qi2r Qi1r Qi1r Qi1r Qi1r Qi1r Qi1r Qi2 Qi2 Qi2 Qi2 Qi2 Qi2 Qi2 Qi3r Qi3r Qi3r Qi3r Qi3r Qi3r Qi3r Qi3r Qi3r Qi3r Qi3r Qi3r Qi3r Qi3r Qi3r Qy4r Qy4r Qy4r Qy4r Qy4r Qy4r Qy4r Qy4r Qy4r Qy4r Qy2r Qy2r Qy2r Qy2r Qy2r Qy2r Qy2r Qy2r Qi2r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy3r Qy4r Qy3r Qy4r Qy4r Qy2r Qy3r Qy2r Qy2r Tt Qy2r Qy3r Tb Tb Qi3r Qy2r Qy2r Qy2r Qy3r Qyc Qy4r Qy4r Qy3r Qy2r Qi3r Qy3 Qy3 Qy3 Qy2 Qy2 Qy2 Qy2 Qy3 Qy3 Qy2 Qy2 Qy3 Qy2 Qy2 Qi3r Qi3ra Qy3r Qy2r Qy3r Qi3r Qi3r Qy2r Qy3r Qy2r Qy4r Qy3r Qy3r Qy2r Qi3r Qi3ra Qi3rb Qi3ra Qi3rb Qi3r Qi3r Qi3r Qi3r Qy4r Qy4r Qy3r Qy3r Qy2r Qy2r Qi3r Qy2r Qy4r Qy4r Qy4r Qy4r Qi3ra Qi3rb Qy2r Qyc Qy3 Qy2 Qi3rb Qy2r Qy3r Qy3r Qy3r Qi3rb Qi1r Qy2r Qi3r Qi2r Qi3r Qy3r Qy3r Qy2 Qy3r Qy3r Qy4r Qy3r Qy3r Dm Qy3r Qy4r Qyc Qy4r Qy3r Tb Qycr Qy1r Qyc Qy2 Tb Qycr Qy4r Qycr Qycr Qycr Qycr Qy1r Qycr Qy1r Qycr Qycb Qycb Qycb Qycb Tb Tb Tb Qycb Qy2 Qy4r Qi3ra Qy3r Qy2 Qycr Qy2r Qy2 Tb Qi2r Qi1r Qy4r Qy3r Qy3 Qi1 Qycb Tb Qy2r Qy3r Qy4r Qy3r Qi3r Qy1r Qy2 Qycr Qy3 Qy2 Qi1 Qy4r Qy4r Qycb Qy3r Qy1 Qy3r Qy3r Qi3 Xb Xb Xb Qy3 Qyc Qyc Qy3 Qy3 Qyc Qyc Qyaf Qls Qls Dm Qyaf Qls Qtc Qi3 Qyaf Qls Qi2r Qls Qi1r Qi3r Qi3r Qo3r Qi1 Qtc Qi2r Qi1r Qi1r Qi1r Qi2 Qi2 Qi3r Qi3r Qi3r Qi3r Qi3r Qi2 Qi2 Qi3r Qycr Qi1r Qi1r Qi3r Qi3r Qi3r Qy3r Qy3r Qy3r Qy2r Qy4r Qy4r Qy2r Qy3r Qy3r Qy2r Qy3r Qy3r Qy3r Qy4r Qy1r Qy3r Qy2r Qy4r Qy2r Qy3r Qy2r Qy4r Qy4r Qy4r Qy4r Qy2r Qy3r Qy2r Tb Tb Tb Tb Tb Tb Tt Tt Tt Tla Tla Xms D_ D_ D_ Qyc 4 32000 4 33000 4 34000 4 35000 4 36000 4 37000 4 38000 4 39000 4 40000 4 32000 4 33000 4 34000 4 35000 4 36000 4 37000 4 38000 4 39000 4 40000 37 93000 37 94000 37 95000 37 96000 37 97000 37 98000 37 99000 38 00000 38 01000 38 02000 38 03000 38 04000 38 05000 38 06000 37 93000 37 94000 37 95000 37 96000 37 97000 37 98000 37 99000 38 00000 38 01000 38 02000 38 03000 38 04000 38 05000 38 06000 0 1 2 0.5 Miles PIMA COCONINO MOHAVE GILA YAVAPAI YUMA PINAL MARICOPA COCHISE LA PAZ GRAHAM APACHE NAVAJO GREENLEE SANTA CRUZ L Example of bedrock canyon confined Holocene Verde River deposits in the Wild and Scenic Verde River, downstream of the Verde Valley. Here the active and flood channel make up much of the canyon bottom. Preserved river deposits are more susceptible to inundation, undercutting, and erosion than in unconfined reaches. High standing Pleistocene Verde River deposits are perched atop bedrock cliffs well above the modern channel. Here. tributaries to the Verde are also incised into bedrock and exhibit narrow, confined channel bottoms and preserved Holocene river terraces. Qy 4 r Qy 3 r Qy 2 r Qy 1 r Qi 1 r Qi 2 r Qi 3 r Qy c r River alluvium Late Holocene Holocene Pleistocene Quaternary Pliocene Miocene Tertiary present day 10,000 y 2.6 My Piedmont alluvium Qyc Qy 2 Qy 3 Qy 1 Qi 3 Qi 2 Qi 1 Qo Qtc Qys d Qi 2 a Qi 2 b QTa Tvg Tvl Qyaf plowed Tsy Holocene/Pleistocene boundary Focus of AZGS mapping Qor QTo Tvv Tvu 5 My Correlation diagram for surficial mapping units in the mapping area. Various bedrock units compiled from existing maps not shown. New surficial mapping of Holocene river alluvium was conducted along the entire length of each channel and combined with a compilation of existing AZGS and USGS geologic mapping. Boundaries of Holocene river alluvium were verified through extensive field work and map analysis. We collected GPS control points, digital photos, and made field observations at the lateral margins of Holocene river alluvium at approximately 1 mile intervals along each side of the river. We used standard geologic nomenclature (solid, dashed and dotted lines) to depict the positional uncertainty of the lateral limits of Holocene river alluvium. Where they exist and have been investigated, archaeological sites, paleontological remains, and other dated organic material provide direct numerical age estimates for Holocene and latest Pleistocene deposits. We reviewed the records of these investigations and visited several of the sites in the field. Dated archaeological material buried in terrace fills provide a maximum age for the overlying deposits and geomorphic surface, whereas dated archaeological material on a terrace tread surface provide a minimum age for the underlying deposits. Summary Through the course of developing and implementing repeatable standards for mapping the extent of Holocene alluvium for ADWR the entire length of the Verde River has been mapped consistently. The depiction of boundary uncertainties has been uniformly applied over the course of the Verde River and 5 major tributaries. The width of Holocene river alluvium varies dramatically with the geologic and geomorphic setting. Comparing our recent mapping with pre-existing maps covering the same area in Verde Valley showed agreement in the extent of Holocene Verde River alluvium in most areas but changed the lateral extent in others. We attribute these differences to substantially better available aerial imagery, mapping in a GIS environment, and the use of field-collected GPS control points. Although our mapping consistently depicts surface relationships it does not address potential subsurface complexities such as burial of distal Holocene river alluvium by onlapping tributary or piedmont deposits. Thickness of Holocene river alluvium likely varies depending on width of the river corridor but generally we think Holocene river deposits are thin. River deposits alternately overlie basin filling sediments and bedrock. The underlying unit may be exposed in narrow canyon reaches. These strip maps provide a fairly detailed description of the physical characteristics of riparian corridors in Arizona. AZGS mapping of the Holocene river alluvium is an important component of subflow delineation but is not the same as subflow delineation as determined by ADWR. Previous AZGS mapping along the San Pedro River in southern Arizona has been used to delineate subflow zones and is currently under adjudication. Whether AZGS mapping along the Verde River will be used in future adjudications pertaining to water rights in central Arizona is yet to be determined. Acknowledgments Funding for this project was provided by the Arizona Department of Water Resources. Access along the Wild and Scenic portion of the Verde River was made possible by rangers with the Coconino National Forest. Well-rounded Verde River cobbles overlain by poorly sorted angular locally derived clasts indicate burial of river alluvium by onlapping piedmont deposits. The lateral extent of the river deposit beneath the fan deposit is unknown. Sycamore Creek joins the lower Verde in the Fort McDowell Yavapai Nation. Sediment from Sycamore Creek and nearby fans overlie distal Verde River Holocene alluvium. Although a likely maximum lateral extent of Holocene river alluvim could be assigned near the base of bounding basin fill hills, our maps depict surface relationships only. Schematic cross section of geomorphic relationships between Tertiary basin fill sediments (units Tvm, Tvl, Tsy), Pleistocene piedmont and river deposits (units Qi n , Qi n r, Qo n r), and Holocene piedmont and river deposits (units Qy n and Qy n r). Qi2 Qi3 Qy2r Qy3r Qy4r Qy3r Qy2r Qy1r Qi3r Tvm Qycr Qy2 Qy2 fan deposits onlap onto Holocene river deposits in subsurface Holocene river boundary as mapped on surface Basin fill sediments (Tvm Tvl, Tvf, Tsy, etc) underlie younger capping piedmont and axial river sediments Tvm Holocene river boundary as mapped on surface Holocene river terraces may or may not exhibit matching deposits on both sides of the river Incised piedmont drainage enters valley Tvm Qor ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Qycb Qy4r Qy4r Qy3r Ps Ps Ps lined channel . . . . . . . . . . . Tb Tb Pc Pc Ps Ps Schematic cross section of geomorphic relationships in narrow bedrock canyon sections. Deposits are bound by steep bedrock walls, terraces are generally thin, channel sediments are coarse, and bedrock may be exposed locally in the channel bottom. Subsurface relations are not well constrained and likely vary along the river course. Older river terraces - Qy1r • Higher in landscape than Qy2r terraces • Fine grained with gravel to cobble lenses • Better soil development, minor soil carbonate accumulation • May have different vegetation populations than Qy2r terraces Factor Holocene Pleistocene Surface character Brown to gray, minimal or no rock varnish Brown to reddish brown, reddish or brown rock varnish Soil development Weak to moderate cambic horizons, slight calcium carbonate accumulation Moderate to strong, clay argillic horizons, obvious calcic carbonate Vegetation Hydro- or meso-riparian Desert scrub Height above river channel 0 to 30 feet 50 to 700 feet Terrace/landform shape Planar, sharp vertical walls where undercut/incised Planar to broadly crowned on top, rounded to well rounded near edges Holocene vs. older deposits Factor River Tributary/piedmont Gravel character Diverse lithology, many well rounded Limited lithologic mix, subangular to angular Overbank (terrace) deposits Thick, generally fine sand, silt, and clay with minor fine gravel layers, weakly developed buried soils Generally thinner, poorly sorted fine gravel to silt Landform slope Low gradient, subparallel to river channel Higher gradient, slopes toward river River vs. tributary deposits Holocene river cobbles Holocene piedmont fan onlap Tb Qycr Qy1r Qy2r Qy3r Tb Dm Qtc AZGS River Mapping 11/2008 - 06/2010 Sycamore Creek Verde River

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Page 1: AZGS Document Repository - Mapping of River Alluvium Along ...repository.azgs.az.gov/sites/default/files/dlio/files/nid1317/gsa_2011... · mapping as well as the availability of higher

Abstract Introduction Methods

Geologic mapping is a primary function of the AZGS, so in cooperation with Arizona Department of Water Resources (ADWR) staff we have established procedures and protocols for documenting and mapping the extent of Holocene floodplain alluvium along rivers in Arizona. These practices were first conducted along the entire length of the San Pedro River, Babocomari River, and Aravaipa Creek (AZGS DM-RM-1). More recent mapping efforts have resulted in new and updated surficial geologic mapping covering over 370 river miles depicted in 2-mile-wide strip maps centered on the Verde River and each major tributary. The maps and reports (AZGS DM-RM-2, DM-RM-3) describe river and tributary deposits of Holocene to late Pliocene age, Pliocene and older basin filling deposits, and various bedrock units along the river at a scale of 1:24,000. Several existing AZGS 7 ½’ quadrangle geologic maps in the Verde Valley were updated and re-released based on this new mapping as well as the availability of higher resolution aerial imagery. The strip maps provide basic information on the geology of the river corridors that may be used in future water rights adjudications and define the physical setting of the river systems.

Mapping of River Alluvium Along the Verde River and Major Tributaries, Central ArizonaCook, Joseph P.1, Pearthree, Philip A.1, House, P. Kyle2, Bigio, Erica3, Onken, Jill A.3, and Youberg, Ann1

1Arizona Geological Survey, 2United States Geological Survey, 3Department of Geosciences, University of Arizona

New mapping widens Holocene alluvium from 600 - 1700 feet depending on interpretation of unit CT2 (AZGS OFR 93-16)

Close agreement between old and new mapping results in very minor changes in lateral extent of Holocene alluvium.

Mapping strategy:

• Compilation of existing geologic mapping in an ArcGIS framework

• Re-evaluation and revision of existing mapping using aerial photos and topographic data

• New mapping of Holocene river alluvium where no large-scale geologic mapping had been conducted previously

• Field-checking of the boundaries of Holocene alluvium in various geologic environments along the river, including systematic collection of GPS field points with observations and ground photos • Depiction of all Holocene river alluvium units on 1:24,000-scale strip maps associated with this report

In 2010, the Arizona Geological Survey (AZGS) released a series of 1:24,000-scale geologic strip maps showing the extent of Holocene channel and floodplain deposits along the Verde River and five large tributaries in central Arizona. The primary purpose of this mapping was to contribute to the legal differentiation of river subflow from groundwater in surrounding areas, as Arizona courts have established the lateral extent of Holocene river alluvium as a key component in delineating subflow zones. These maps also define the physical architecture and geomorphic framework of the river systems, depicting river and tributary deposits of Holocene to late Pliocene age, Pliocene and older basin filling deposits, and various bedrock units. We employed standard geomorphic and geologic criteria to differentiate and map river and tributary alluvial deposits of different ages. The degree of clast rounding, lithologic diversity, and landform/terrace slope were used to differentiate river from piedmont alluvium.

The through-flowing Verde River developed several million years ago, linking several closed or partially integrated basins. When the Verde River became integrated, it began to downcut along its entire course, and this in turn drove deep incision along all of its major tributaries. The maximum amount of incision has probably occurred along the middle Verde River in Verde Valley, where the river has incised at least 300 m below the former valley floor since the late Pliocene. High standing relict terrace deposits all along the Verde River record former river levels through the Pleistocene. Because the Verde River and its tributaries have incised deeply into both bedrock and less-resistant sedimentary basins, the lateral extent of Holocene river alluvium varies dramatically from less than 30 m to over 1 km across. Within this corridor, we mapped up to 6 Holocene units, including active channels, bedrock-lined active channels, flood channels, and several levels of terraces. The extent of active channels, flood channels and low bars change with virtually every large flood. Young terraces are more stable, and typically are subject to shallow inundation in floods. Dates from archaeological sites and paleoflood studies suggest that nearly all of the Holocene deposits along the river are less than 4 ka.

Qy3r

Qy4r

Qy4r

Qy2r

Dm

TbTb

Dm

Qycr

Distribution of Holocene river alluvium in narrow bedrock canyon reach in the upper Verde River near Paulden, AZ. All preserved Holocene river terraces are narrow and bound by tall bedrock walls and onlapping colluvium.

We t B e a v e r C r e e k

We s t C

l e a r C r e e k

Fo s s i l

C re e k

E a s t V

e r d e Ri v

er

Coconino

Yavapai

Gila

Maricopa

ChinoValleyNorth

Clarkdale

OFR95-16

Studyarea

Cottonwood Cornville

PageSprings

MiddleVerde

CampVerde

HornerMountain

HorseshoeDam

BartlettDam

MaverickMountain

FortMcDowell

O a k C r e e k

Footprint of two mile wide map corridor centered on Verde River and mapped tributaries (AZGS DM-RM-2, and 3). Blue boxes represent previous AZGS mapping, the yellow box represents concurrent AZGS mapping. Compilation of existing USGS bedrock mapping outside AZGS mapped areas was also conducted.

Qycr

Qy2r

Qy4r

Distribution of Holocene river alluvium in an unconfined reach in the Fort McDowell Yavapai Nation. Flood channel (Qy4r) terraces are extensive and lightly vegetated. Qy2r terraces are often obscured by agricultural use. Holocene river alluvium is bound by onlapping alluvial deposits and eroded basin fill deposits.

Pleistocene river terraces - Qi1r, Qi2r, Qi3r• Clay rich, reddened soil horizons• Obvious CaCO3 accumulation• Planar to moderately rounded• Stand high in the landscape relative to the modern river

A Pleistocene Verde River deposit capping basin filling sediments near the Verde/Salt confluence stands 165 feet above the modern channel.

Pleistocene cap

Verde River

Active channels - Qycr• Unconsolidated sand to cobbles• Pool and riffle sequences• Lined by riparian trees and vegetation• Commonly submerged

Young river terraces - Qy2r• Higher in landscape than Qy3r terraces• Generally fine grained with gravel lenses• Some soil development, minor soil carbonate accumulation• Typically are presently or were historically plowed and irrigated; many now developed• Usually most laterally extensive terrace

Dm

Incised Qy2r in upper Verde

Floodplain / low terraces - Qy3r• Higher than Qy4r surfaces• Only inundated during more extreme flow• Riparian trees and grasses• Former floodplain and river meanders• Mild soil development

Qy3r

Qycr

Flood channels - Qy4r• Adjacent to Qycr deposits• Inundated under higher flow (seasonal or flood)• No soil development• Unvegetated to lightly vegetated• Often show signs of recent flooding

Qycr

Qy4r

Qyc

Qyc

Qyc

Qyc

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TvmQys

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d

Qi2r

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Tvm

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Qy3rQy4r

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Qo3r

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Qi1

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Qi1ra

Tvg

Tvl

Qis

Qi2

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Tvm

Tvm

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d

Qo2

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Qi1

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Qo2

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Qi2r Qo3r

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Qi1ra

Qi2r

Qi2r

Qo3r

Qo3r

Qi1r

QTo

Tvg

Tvg

Tvg

Tvg

Qi1rbTvg

Qis

Qis

Qi2

Qi2

Qis

Qis

Qi2

Tvg

Tvl

Qis

Tvm

Tvm

Tvm

Qi3r

Tvm

Tvm

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Tvm

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Tvm

Tvm

Qi3r

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Tvm

Tvm

Qi3r

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Tvm

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QTo

Qi2

Tvm

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Tvm

Tvm

Tvm

Tvm

Qy4r

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Qy2rQy1r

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Qy3r

Qy3r

Qy2r

Qy2r

Qy1r

Qy4r

Qy4r

Qy4r

Qy2r

Qy4r

HV 700

HV 326

HV 192

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HV 193

HV 194

HV 426

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HV 191HV 177

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HV 176HV 175

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HV 186

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HV 167

418000 419000 420000 421000 422000 423000 424000 425000 426000 427000

418000 419000 420000 421000 422000 423000 424000 425000 426000 427000

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PIMA

COCONINOMOHAVE

GILA

YAVAPAI

YUMA PINAL

MARICOPA

COCHISE

LA PAZ

GRAHAM

APACHENAVAJO

GREENLEE

SANTA CRUZ

L

0 1 20.5Miles

Example of laterally extensive Holocene Verde River deposits in the Verde Valley, central Arizona. The Verde River incising into the relatively erodible Verde Formation (lacustrine, mudstone, limestone, gypsum, and diatomite deposits) has resulted in widespread Holocene deposit preservation. The active channel represents only a small part of the river system with much wider flood channel deposits and extensively preserved young terraces. Tributary deposits grade to similarly aged river terraces and in some places cover them. Lateral topographic constraints are composed of older river deposits, eroded basin fill deposits, or onlapping tributary alluvium.

HV 512

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HV 501

HV 286

HV 287

HV 343

HV 720

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HV 342HV 718

HV 341

HV 340

HV 717

HV 339

Qy2

Qyc

Qy3

Qy3

Qy3

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Qy3Qy3

Qy3

Qyaf

Qy2

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Qy2

Qy2

Qls

Qi3

Qi1

Qi1

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Tb

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Qy3rQy2rQi3r

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Qy2Qy2

Qy3Qy3

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Qy3

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Qy2

Qi3r

Qi3raQy3r

Qy2rQy3r

Qi3r

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Qi3r

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Qi3rbQi1r

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Qi3r

Qi2r

Qi3r

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Qy3rQy2

Qy3r

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Qy3r

Dm

Qy3r

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Tb

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QycQy2

Tb

Qycr

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Qycb

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Tb

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Qycr

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Qy2

Tb

Qi2r

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Qi1

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Tb

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Qtc

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Qi2Qi3r

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Qy3r

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Tb

Tb

Tb

Tb

Tb

Tb

Tt

Tt

Tt

Tla

Tla

Xms

D_D_

D_

Qyc

432000 433000 434000 435000 436000 437000 438000 439000 440000

432000 433000 434000 435000 436000 437000 438000 439000 440000

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0 1 20.5Miles

PIMA

COCONINOMOHAVE

GILA

YAVAPAI

YUMA PINAL

MARICOPA

COCHISE

LA PAZ

GRAHAM

APACHENAVAJO

GREENLEE

SANTA CRUZ L

Example of bedrock canyon confined Holocene Verde River deposits in the Wild and Scenic Verde River, downstream of the Verde Valley. Here the active and flood channel make up much of the canyon bottom. Preserved river deposits are more susceptible to inundation, undercutting, and erosion than in unconfined reaches. High standing Pleistocene Verde River deposits are perched atop bedrock cliffs well above the modern channel. Here. tributaries to the Verde are also incised into bedrock and exhibit narrow, confined channel bottoms and preserved Holocene river terraces.

Qy4r

Qy3r

Qy2r

Qy1r

Qi1r

Qi2r

Qi3r

Qycr

River alluvium

LateHolocene

Holocene

Pleistocene

Quate

rnary

Pliocene

Miocene

Te

rtia

ry

presentday

10,000 y

2.6 My

Piedmont alluvium

Qyc

Qy2

Qy3

Qy1

Qi3

Qi2

Qi1

Qo

Qtc Qys

d

Qi2aQi2b

QTa

Tvg Tvl

Qyaf

plowed

Tsy

Holocene/Pleistocene boundary

Focusof AZGSmapping

Qor

QTo

TvvTvu

5 My

Correlation diagram for surficial mapping units in the mapping area. Various bedrock units compiled from existing maps not shown.

New surficial mapping of Holocene river alluvium was conducted along the entire length of each channel and combined with a compilation of existing AZGS and USGS geologic mapping. Boundaries of Holocene river alluvium were verified through extensive field work and map analysis. We collected GPS control points, digital photos, and made field observations at the lateral margins of Holocene river alluvium at approximately 1 mile intervals along each side of the river. We used standard geologic nomenclature (solid, dashed and dotted lines) to depict the positional uncertainty of the lateral limits of Holocene river alluvium.

Where they exist and have been investigated, archaeological sites, paleontological remains, and other dated organic material provide direct numerical age estimates for Holocene and latest Pleistocene deposits. We reviewed the records of these investigations and visited several of the sites in the field. Dated archaeological material buried in terrace fills provide a maximum age for the overlying deposits and geomorphic surface, whereas dated archaeological material on a terrace tread surface provide a minimum age for the underlying deposits.

Summary

Through the course of developing and implementing repeatable standards for mapping the extent of Holocene alluvium for ADWR the entire length of the Verde River has been mapped consistently. The depiction of boundary uncertainties has been uniformly applied over the course of the Verde River and 5 major tributaries. The width of Holocene river alluvium varies dramatically with the geologic and geomorphic setting. Comparing our recent mapping with pre-existing maps covering the same area in Verde Valley showed agreement in the extent of Holocene Verde River alluvium in most areas but changed the lateral extent in others. We attribute these differences to substantially better available aerial imagery, mapping in a GIS environment, and the use of field-collected GPS control points.

Although our mapping consistently depicts surface relationships it does not address potential subsurface complexities such as burial of distal Holocene river alluvium by onlapping tributary or piedmont deposits. Thickness of Holocene river alluvium likely varies depending on width of the river corridor but generally we think Holocene river deposits are thin. River deposits alternately overlie basin filling sediments and bedrock. The underlying unit may be exposed in narrow canyon reaches. These strip maps provide a fairly detailed description of the physical characteristics of riparian corridors in Arizona.

AZGS mapping of the Holocene river alluvium is an important component of subflow delineation but is not the same as subflow delineation as determined by ADWR. Previous AZGS mapping along the San Pedro River in southern Arizona has been used to delineate subflow zones and is currently under adjudication. Whether AZGS mapping along the Verde River will be used in future adjudications pertaining to water rights in central Arizona is yet to be determined.

Acknowledgments

Funding for this project was provided by the Arizona Department of Water Resources. Access along the Wild and Scenic portion of the Verde River was made possible by rangers with the Coconino National Forest.

Well-rounded Verde River cobbles overlain by poorly sorted angular locally derived clasts indicate burial of river alluvium by onlapping piedmont deposits. The lateral extent of the river deposit beneath the fan deposit is unknown.

Sycamore Creek joins the lower Verde in the Fort McDowell Yavapai Nation. Sediment from Sycamore Creek and nearby fans overlie distal Verde River Holocene alluvium. Although a likely maximum lateral extent of Holocene river alluvim could be assigned near the base of bounding basin fill hills, our maps depict surface relationships only.

Schematic cross section of geomorphic relationships between Tertiary basin fill sediments (units Tvm, Tvl, Tsy), Pleistocene piedmont and river deposits (units Qin, Qinr, Qonr), and Holocene piedmont and river deposits (units Qyn and Qynr).

Qi2Qi3

Qy2rQy3r

Qy4rQy3r

Qy2rQy1r Qi3r

Tvm

QycrQy2

Qy2 fan depositsonlap onto Holocene

river deposits in subsurface

Holocene riverboundary as mapped

on surfaceBasin fill sediments

(Tvm Tvl, Tvf, Tsy, etc) underlieyounger capping piedmont

and axial river sediments

Tvm

Holocene riverboundary as mapped

on surface

Holocene river terracesmay or may not exhibit matching deposits onboth sides of the river

Incised piedmontdrainage enters

valley

Tvm

Qor

??

? ??

??

???????

??

???

??

Qycb

Qy4rQy4rQy3r

Ps Ps

Ps lined channel

..

... .

.. .

..

Tb Tb

Pc Pc

PsPs

Schematic cross section of geomorphic relationships in narrow bedrock canyon sections. Deposits are bound by steep bedrock walls, terraces are generally thin, channel sediments are coarse, and bedrock may be exposed locally in the channel bottom. Subsurface relations are not well constrained and likely vary along the river course.

Older river terraces - Qy1r• Higher in landscape than Qy2r terraces• Fine grained with gravel to cobble lenses• Better soil development, minor soil carbonate accumulation• May have different vegetation populations than Qy2r terraces

Factor Holocene Pleistocene Surface character Brown to gray, minimal or

no rock varnish Brown to reddish brown, reddish or brown rock varnish

Soil development Weak to moderate cambic horizons, slight calcium carbonate accumulation

Moderate to strong, clay argillic horizons, obvious calcic carbonate

Vegetation Hydro- or meso-riparian Desert scrub

Height above river channel

0 to 30 feet 50 to 700 feet

Terrace/landform shape

Planar, sharp vertical walls where undercut/incised

Planar to broadly crowned on top, rounded to well rounded near edges

Holocene vs. older deposits

Factor River Tributary/piedmont Gravel character Diverse lithology, many

well rounded Limited lithologic mix, subangular to angular

Overbank (terrace) deposits

Thick, generally fine sand, silt, and clay with minor fine gravel layers, weakly developed buried soils

Generally thinner, poorly sorted fine gravel to silt

Landform slope Low gradient, subparallel to river channel

Higher gradient, slopes toward river

River vs. tributary deposits

Holocene river cobbles

Holocene piedmont fan onlap

Tb

Qycr

Qy1rQy2r

Qy3r

Tb

Dm

Qtc

AZGS River Mapping11/2008 - 06/2010

Sycamore Creek

Verde River

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Arizona Geological Survey - repository.azgs.az.gov