Michelle Trogdon

GEOG 5401 Soils GeographyFall 2007 – Univ of Colorado, Boulder

• analyze 1 soil profile associated with features• to distinguish features in eroding contexts• soil chemistry• sifting through bad photos without scales• aid future Master’s project

• Oaxaca• Mixteca Alta• Nochixtlan Valley

• refers to leveled land on otherwise hillslope • method of soil conservation• mitigate erosion• water and nutrients• residential, agricultural terraces, both?

Formative (900BC-AD200)• agricultural production begins in Mixteca• population dispersed on low piedmontClassic (AD200-800)• hilltop towns are established• population expandsPostclassic (AD 800-1450)• caciques (codices)• commoner farmers• increased terraced landscape around cacicazgos

• No significant type change through Classic-Postclassic• When did retention terraces begin in Formative?• previously buried now eroding may provide insight into agricultural adaptation• clearing land creates erosion• El Palmillo (V. of Oaxaca) “paved” terraces increases runoff• semi-arid environment and high clay content odds for shrink-swell, need to control soil moisture

• informal “rock-piling” of river rocks 5-30 cm upslope• wider base , ~1m above soil surface• boulders 40-50cm downslope (drystone)• 1-3m below soil surface• chronological congruency• Ethno evidence- still in use today• Labor community-levelor few households

• natural fill, multiple events• backfill• Stratigraphy indicators• Soil dating• balance of moisture, nutrients• Nitrogen, phosphorous• Semi-arid more CaCO3, fixes PO4• adding N makes plants (grasses) more efficient with less water• N fixers require more P

Table 1. The features measured in this study.      

Site Feature Length Maxium Minimum Artifacts Style

    (cm) Height (cm)Height (cm)    

Etlatongo F1 80 20 20 none small pebbles

diagonal

Yanhuitlan F1 100 15 7 pottery loose angular cobbles

3-10 cm

Yanhuitlan F11 125 40 15 none large rounded cobbles

5-15 cm

Yucuita F7 750 40 20 none row of large boulders

Yucuita F1 130 90 70 nonelarge range of size cobbles

           to boulders, ontop of gravel

• On top of Paleosol 4• Radiocarbon dates from soils 600-8520BC• blocky structure = more clay, drier climate• more CaCO3= more PO4

P3

P4

1. Reduce runoff erosion and retain some water and nutrients

2. Reduce collecting water saturating clay-rich soil and damaging soil quality

• soil info• date• PO4 and pH• soil indicators upslope and downslope

• More details regarding relationship to soils• orientation of walls = erosion patterns and stream migration• associated soils throughout valley, erosion and deposition events• excavation of coeval terraces on hilltops and valley floors • practices vary with time or topography