Surficial Geologic Map of the Mount Hopkins and Northern Part of the San Cayetano ...repository.azgs.az.gov/sites/default/files/dlio/files/... · 2011. 5. 13. · Part of San Cayetano
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111°0'0"W 111°0'0"W 110°57'30"W 110°57'30"W 110°55'0"W 110°55'0"W 110°52'30"W 110°52'30"W 31°35'0"N 31°35'0"N 31°37'30"N 31°37'30"N 31°40'0"N 31°40'0"N 31°42'30"N 31°42'30"N 31°45'0"N 31°45'0"N Methods and Sources of Information A preliminary map was prepared by transferring geologic contacts mapped from color infrared aerial photographs to 1:24,000 -scale topographic maps as described by Dueholm (1980). Aerial photography was conducted in 1996 under contract by the National Aerial Photography Program at an altitude of 20,000 feet, resulting in 9 X 9 inch photographs at a scale of 1:40,000. Contacts established by photogrammetric methods were then digitized to shapefiles using ArcGIS. ™ After the preliminary map was checked in the field, contacts were modified in ArcGIS ™ using one-meter resolution digital color orthophoto quarter -quadrangles based on the same photography. Geologic units were identified by reference to the map of Helmi ck (1986), which covers much of the mapped area, and by reference and edge -matching to geologic maps of the adjoining Amado and Tubac 7½ ’quadrangles (Youberg and Helmick, 2001) and the Green Valley 7½’quadrangle (Pearthree and Youberg, 2000). Nomenclature for Quaternary units is based on that of Youberg and Helmick (2001), who describe the units in detail. Additional information on description of map units is given by Helmick (1986). Some structural features were adapted from the 1:48,000 -scale geologic map by Drewes (1971). Field checking of units was done during two weeks in February and March of 2005. Some faults and contacts not identified previously were mapped in the field. Map Explanation Descriptions and ages for units Qy, Qy1, Qiy, Qi 3, Qi2, Qo, and QTs are from Youberg and Helmick (2001). Several units described and mapped by Youberg and Helmick (2001) and Pearthree and Youberg (2000) were not mapped separately. Most Holocene sediment in active piedmont washes was not subdivided, except locally where small terraces 1-2 m above stream level were identified as older Holocene alluvium (unit Qy 1). Older Holocene alluvium is especially widespread in low terraces adjoining major washes, including Chino and Josephine Canyons. Late Pleistocene alluviu m (unit Qi 3), well-developed in terraces along most piedmont washes, was also not subdivided. Several terrace levels of Late Pleistocene alluvium can be distinguished locally but consist of unpaired terrace elements, deposited as the stream shifted from valley side t o side during minor down-cutting. Such levels, formed by channel shifting, were not deemed consistent enough to subdivide. Unit Descriptions Piedmont Alluvium Undifferentiated Holocene alluvium (<~10 ka) Unit Qy consists of undifferentiated active or recently active alluvium found in smaller incised drainages on the piedmonts and more extensive young alluvial fans at the base of the piedmonts, adjacent to the Santa Cruz floodplain. Soil development varies from no to weakly developed cambic horizons over weak to moderate (stage I to II) calcic horizons. This map unit includes units Qy 2, Qy1, and Qy of Youberg and Helmick (2001), units Q5 and Q4 of Helmick (1986), and units 3B and 4 of Pearthree and Calvo (1987). Holocene alluvium (~2 to ~10 ka) Unit Qy1 consists of low terraces found at scattered locations along incised drainages on the piedmonts. Qy 1 surfaces are slightly higher and less subject to inundation than adjacent Qy surfaces. Surfaces are generally planar; local relief may be up to 1 m where gravel bars are present, but typically is much less. Qy 1 surfaces are less than 2 m above adjacent active channels. Surfaces typically are sandy but locally have unvarnished, open, fine gravel lags. Qy 1 surfaces generally appear fairly dark on aerial photos, but where a gravel lag is present, surfaces are light colored. Channel patterns on alluvial fans are weakly integrated distributary (branching downstream) systems. Qy 1 soils typically are weakly developed, with some soil structure but little clay and stage I to II calcium carbonate accumulation (see Machette, 1985, for description of stages of calcium carbonate accumulation in soils). This map unit includes units Q4 of Helmick (1986). Holocene to Late Pleistocene alluvium (<~130 ka) Broadly rounded alluvial fan surfaces approximately 1 m above active channels composed of mixed alluvium of late Pleistocene and Holocene age. Drai nage networks consist of a mix of distributary channel networks associated with larger drainages and tributary channels associated with smaller drainages that head on Qiy surfaces. Qiy areas are primarily covered by a thin veneer of Holocene fine-grained alluvium (unit Qy), but reddened Pleistocene alluvium (unit Qi 3 and rarely, Qi2) is exposed in patches on low ridges and in roads and cut banks of washes. The Holocene surfaces usually are light brown in color and soils have weak subangular blocky structure and minor carbonate accumulation. This unit is labeled Qly in Youberg and Helmick (2001) and is generally correlative with units 2d and 3a of Pearthree and Calvo (1987). Late Pleistocene alluvium (~10 to ~130 ka) Unit Qi3 consists of slightly to moderately dissected relict alluvial fans and terraces found on the upper, middle and lower piedmont. Moderately to well -developed, slightly to moderately incised tributary drainage networks are typical on Qi 3 surfaces. Active channels are incised up to about 2 m below Qi3 surfaces, with incision typically increasing toward the mountain front, and towards the southern end of the Santa Cruz Valley. Qi 3 fans and terraces are commonly lower in elevation than adjacent Qi 2 and older surfaces, but the lower margins of Qi3 deposits lap out onto more dissected Qi 2 surfaces in some places. Qi 3 deposits consist of pebbles, cobbles, and finer-grained sediment. Qi 3 surfaces commonly have loose, open lags of pebbles and cobbles; surface clasts exhibit weak rock varnish. Qi 3 surfaces appear light orange to dark orange on color aerial photos, reflecting reddening of surface clasts and the surface soil horizon. Qi 3 soils are moderately developed, with orange to reddish brown clay loam to light clay argillic horizons and stage II calcium carbonate accumulation. Unit Qi 3 is labeled Ql, Ql 1 and Ql2 in Youberg and Helmick (2001) and is correlative with unit Q3 of Helmick (1986) and unit 2d of Pearthree and Calvo (1987). Middle Pleistocene alluvium (~130 to ~750 ka) Unit Qi2 consists of moderately to highly dissected relict alluvial fans and terraces with strong soil development found throughout the map area. Qi 2 surfaces are drained by well-developed, moderately to deeply incised tributary channel networks. Channels are typically sever al meters below adjacent Qi 2 surfaces with channel dissection increasing towards the mountains and the southern end of the map area. Well -preserved, planar Qi 2 surfaces are smooth with scattered pebble and cobble lags; surface color is reddish brown; rock varnish on surface clasts is typically orange or dark brown. More eroded, rounded Qi 2 surfaces are characterized by scattered cobble lags with moderate to strong varnish and broad ridge-like topography. Well-preserved Qi 2 surfaces have a distinctive dark red color on color aerial photos, reflecting reddening of the surface soil and surface clasts. Soils typically contain reddened, clay argillic horizons, with obvious clay skins and subangular to angular blocky structure. Underlying soil carbonate development is typically stage II-III, with abundant carbonate through at least 1 m of the soil profile; indurated petrocalcic horizons are rare. Carbonate development is stronger towards the north end of the map area, and in areas where carbonate parent material exists. This unit is labeled Qm in Youberg and Helmick (2001) and is generally correlative to unit Q2 of Helmick (1986) and unit Q2b of Pearthree and Calvo (1987). Early Pleistocene alluvium (~750 ka to ~ 2 Ma) Unit Qo consists of very old alluvial fan remnants on top of highly dissected basin fill deposits (unit QTs). Remnant fan surfaces are moderately to well preserved with strong soil development. Qo deposits and fan surface remnants are best preserved on the upper piedmonts near the mountain fronts. Qo deposits consist o cobbles, boulders, and sand and finer clasts. Where surfaces are planar and well-preserved, soils typically have a distinct dark red, heavy clay argillic horizon, and stage III to IV calcic horizons. This map unit is generally correlative to unit Q1 and Q1E of Helmick (1986), and unit Q2a of Pearthree and Calvo (1987). Qo surfaces record the highest levels of aggradation in the Santa Cruz valley, and are probably correlative with other high, remnant surfaces found at various locations throughout southern Arizona (Menges and McFadden, 1981; Pearthree and Calvo, 1987). Pleistocene to Pliocene colluvium (~10 ka to ~5 Ma) Pleistocene to Pliocene colluvium (unit QTc), consisting of unsorted boulders and smaller detritus shed from a fault zone adjacent to Elephant Head, is mapped separately from Early Pleistocene and Pliocene alluvium (unit QTs). Because unit QTc contains a distinct accumulation of boul der detritus on steep slopes immediately below the fault, its age may have a younger range than unit QTs. Unit QTs is overlain (unconformably, in some places) by Early Pleistocene alluvium (unit Qo), and thus has a younger range of Early Pleistocene age. Early Pleistocene to Pliocene alluvium (~750 ka to ~5 Ma) Unit QTs is a basin fill deposit consisting of very old, deeply dissected and highly eroded alluvial fan deposits derived from nearby mountains. QTs surfaces are alternating eroded ridges and deep valleys, with ridge crests typically 10 to 30 meters above adjacent active channels. QTs ridges are more deeply incised towards the mountains and the southern end of the map area. The thickness of QTs deposits varies from a few meters near the mountains to260 m near Amado (Gettings and Houser, 1997). They are drained by deeply incised tributary channel networks. Generally QTs ridges are rounded except where topped by plana remnants of Qo alluvium near the mountain fronts. Pockets of red, well developed soil mantle some of the hillslopes. QTs deposits are dominated by subangular to subrounded boulders, cobbles, and gravels with layers and lenses of sand, silt and clay. Deposits are moderately indurated and are quite resistant to erosion because of the large clast size and carbonate accumulation, which can vary locally from stage III-V (cemented petrocalcic horizons with laminar cap). Other Units Pliocene to Miocene Nogales Formation The Pliocene and Miocene Nogales Formation (Simons, 1974) was mapped in the San Cayetano Mountains quadrangle. The Nogales Formation is distinguished from Early Pleistocene and Pliocene alluvium by its preponderance of volcanic clasts, generally greater induration, more fracturing and faulting, and greater angle of dip. The distinction is clear in the San Cayetano quadrangle, but is not quite so easy to make northward in the Mount Hopkins quadrangle. Drewes (1971 originally mapped the Nogales Formation (which he called “Gravel at Nogales” ) in Cottonwood Canyon and in unnamed canyons to the north, but we consider those strata to be Early Pleistocene and Pliocene alluvium. Undifferentiated bedrock R Tn Qy Qo Qi 2 Qi 3 Qiy Qy 1 QTc QTs Tn Quaternary Tertiary QTs QTc Qy Qo Qi 2 Qi 3 Qiy Qy 1 Stratigraphic Correlation Arizona Geological Survey CM-06-A (Mount Hopkins and Northern Part of San Cayetano Mountains) SCALE 1:24,000 1 0 1 0.5 Miles 1,000 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 500 Feet 1 0 1 0.5 Kilometers Arizona Geological Survey CM-06-A (Mount Hopkins and Northern Part of San Cayetano Mountains) Topographic base from USGS 7½' Mount Hopkins and San Cayetano Mountains quadrangles, compiled from aerial photographs taken 1975; field checked in 1966, edited in 1981. Transverse Mercator projection; NAD 27, UTM zone 12. Magnetic declination 12º30' east of true north. Digital data is also projected in NAD 27, UTM zone 12. Acknowledgements We thank the staff of the Arizona Geological Survey, especially Philip A. Pearthree and Ann Youberg for advice in field identification of map units. References Cited Drewes, Harald, 1971, Geologic map of the Mount Wrightson quadrangle, southeast of Tucson, Santa Cruz and Pima Counties, Arizona: U.S. Geological Survey Miscellaneous Investigations Series Map I-614, scale 1:48,000. Dueholm, K.S., 1980, Computer-supported photointerpretation: Photogrammetria, v. 39, p. 159 -171. Gettings, M.E. and Houser, B.B., 1997, Basin geology of the upper Santa Cruz Valley, Pima and Santa Cruz Counties, Southeastern Arizona; U.S. Geological Survey Open-File Report 97-676, 38 p., scale 1:250,000. Helmick, W.R., 1986, The Santa Cruz River terraces near Tuba c, Santa Cruz County, Arizona: unpublished M.S. thesis, Tucson, University of Arizona, 96 p. Machette, M.N., 1985, Calcic soils of the southwestern United States , in Weide, D.L., ed., Soils and Quaternary Geology of the Southwestern United States: Geological Society of America Special Paper 203, p. 1 -21. Menges, C.M., and McFadden, L.D., 1981, Evidence for a latest Miocene to Pliocene transition from Basin -Range tectonic to post-tectonic landscape evolution in southeastern Arizona: Arizona Geological Socie ty Digest 13, p. 151-160. Pearthree, P.A., and Calvo, S.S., 1987, The Santa Rita fault zone: Evidence for large magnitude earthquakes with very long recurrence intervals, Basin and Range province of southeastern Arizona: Bull. Seis. Soc. Amer., v. 77, p. 97-116. Pearthree, P.A., and Youberg, Ann, 2000, Surficial geologic maps and geologic hazards of the Green Valley -Sahuarita area, Pima County, Arizona: Arizona Geological Survey Open-File Report 00-13, scale 1:24,000, text 21 p. Simons, F.S., 1974, Geologic map and sections of the Nogales and Lochiel quadrangles, Santa Cruz County, Arizona: U.S. Geological Survey Miscellaneous Investigations Series Map I-762, scale 1:48,000. Youberg, Ann, and Helmick, W.R., 2001, Surficial geologic maps and geologic hazard s of the Amado-Tubac area, Santa Cruz and southern Pima Counties, Arizona: Arizona Geological Survey Digital Geologic Map 13, scale 1:24,000. Location Map TUCSON PIMA GILA PINAL MARICOPA COCHISE GRAHAM SANTA CRUZ Arizona Counties Shown; Mapped Area Illustrated In Yellow Map Legend Contact, accurate Contact, approximate @@ Contact, queried where uncertain Z 10 Strike and dip of beds Fault, accurate : Fault, approximate : Arizona Geological Survey 416 W. Congress Street, Suite 100 Tucson, AZ 85701 (520) 770-3500 www.azgs.az.gov § ¨ ¦ § ¨ ¦ § ¨ ¦ 17 8 10 § ¨ ¦ 19 Surficial Geologic Map of the Mount Hopkins and Northern Part of the San Cayetano Mountains 7½' Quadrangles, Santa Cruz and Pima Counties, Arizona by David A. Lindsey and Bradley S. Van Gosen Arizona Geological Survey Contributed Map 06-A (CM-06-A), version 1.0 October, 2006 Citation for this map: Lindsey, D.A. and Van Gosen, B.S., 2005, Surficial Geologic Map of the Mount Hopkins and Northern Part of the San Cayetano Mountains 7½’ Quadrangles, Santa Cruz and Pima Counties, Arizona: Arizona Geological Survey Contributed Map 06-A (CM-06-A), 1 sheet, scale 1:24,000. Not to be reproduced for commercial purposes ^ 12½º MN N 2006 MAGNETIC NORTH DECLINATION PHOENIX
Methods and Sources of Information A preliminary map was
prepared by transferring geologic contacts mapped from color
infrared aerial photographs to 1:24,000 -scale topographic maps as
described by Dueholm (1980). Aerial photography was conducted in
1996 under contract by the National Aerial Photography Program at
an altitude of 20,000 feet, resulting in 9 X 9 inch photographs at
a scale of 1:40,000. Contacts established by photogrammetric
methods were then digitized to shapefiles using ArcGIS. ™ After the
preliminary map was checked in the field, contacts were modified in
ArcGIS ™ using one-meter resolution digital color orthophoto
quarter -quadrangles based on the same photography. Geologic units
were identified by reference to the map of Helmi ck (1986), which
covers much of the mapped area, and by reference and edge -matching
to geologic maps of the adjoining Amado and Tubac 7½ ’ quadrangles
(Youberg and Helmick, 2001) and the Green Valley 7½’ quadrangle
(Pearthree and Youberg, 2000). Nomenclature for Quaternary units is
based on that of Youberg and Helmick (2001), who describe the units
in detail. Additional information on description of map units is
given by Helmick (1986). Some structural features were adapted from
the 1:48,000 -scale geologic map by Drewes (1971). Field checking
of units was done during two weeks in February and March of 2005.
Some faults and contacts not identified previously were mapped in
the field. Map Explanation Descriptions and ages for units Qy, Qy1,
Qiy, Qi3, Qi2, Qo, and QTs are from Youberg and Helmick (2001).
Several units described and mapped by Youberg and Helmick (2001)
and Pearthree and Youberg (2000) were not mapped separately. Most
Holocene sediment in active piedmont washes was not subdivided,
except local ly where small terraces 1 -2 m above stream level were
identified as older Holocene alluvium (unit Qy 1). Older Holocene
alluvium is especially widespread in low terraces adjoining major
washes, including Chino and Josephine Canyons. Late Pleistocene
alluviu m (unit Qi3), well-developed in terraces along most
piedmont washes, was also not subdivided. Several terrace levels of
Late Pleistocene alluvium can be distinguished locally but consist
of unpaired terrace elements, deposited as the stream shifted from
valley side t o side during minor down-cutting. Such levels, formed
by channel shifting, were not deemed consistent enough to
subdivide.
Unit Descriptions Piedmont Alluvium Undifferentiated Holocene
alluvium (
