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Natural Setting

natural context

The Zatopec site is located below the Balcones Escarpment, which is a physical boundary between the Edwards Plateau (Hill Country) to the west and the Blackland Prairie to the east. Transitional regions such as this one, between large-scale environmental zones, are known as ecotones: they are high-energy settings capable of supporting tremendous diversity in terms of plant and animal species.

The natural setting has many components: geomorphological, geological, soil, plant, animal, hydrological, climate, and paleoenvironmental, to name a few. Each of these  factors should be considered as archaeological materials are analyzed.

What is the setting of
Zatopec in terms of . . . (click on each component below to find out more)

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  • Zatopec is situated adjacent to Purgatory Creek, which drains central Texas Hill Country landscapes west and northwest of San Marcos. The site lies at the confluence of three streams: two small, unnamed tributaries and Purgatory Creek. The landform that Zatopec occupies, though obscured by modern construction, gently slopes upward to the east at the base of the Balcones Escarpment. Across the unnamed tributary to the west side of the site, terrain has greater relief, and limestone bedrock containing chert cobbles is exposed in many places. To the south of the site, across the empty channel of Purgatory Creek, the landscape flattens out into the Coastal Plains region.

  • Bedrock geology in the region is complex due to the proximity of the Balcones Fault Zone. Edwards Limestone underies the site, which was mapped by the Bureau of Economic Geology. Soils of this area have been mapped and described by the Soil Conservation Service (now the Natural Resources Conservation Service). The soil types present include Comfort-Rock outcrop complex, Rumple-Comfort association, frequently flooded Orif soils, and Denton silty clay. The differences between these soils are in the landforms that they cover and the vegetation they support. These soils range from shallow to relatively deep, and have variable potentials of containing intact archaeological deposits.

  • Zatopec is located in a transitional zone between two large-scale environmental provinces. As a result, a mixture of plants and animals characteristic of the Hill Country and the Coastal Plains can be found at the site.

    As described by biolgist W. Frank Blair, typical modern fauna found in the region include white-tailed deer, eastern cottontail, raccoon, opossum, and badger. Additionally, armadillo, beaver, black rat, coyote, crayfish, domestic dog, eastern gray squirrel, eastern wood rat, freshwater mussel, gray fox, hispid cotton rat, horse, muskrat, pig, red fox, turkey, western diamond back, and whitetail jackrabbit are among the modern wildlife commonly found in the area. Many, though not all, of these taxa were also present in the prehistoric period and are reflected in the site's inventory of animal remains.

    The region's natural vegetation is generally a grassland-woodland-shrubland mosaic, where grasslands separate patches of woody plants and shrubs. Tall grasses, Osageo range, anaqua, netleaf privet, netleaf hackberry, honey mesquite, and china berry are currently present in the vicinity.

  • San Marcos Springs, known to the historic Tonkawas as Canocanayesatetlo and European settlers as St. Mark's, have attracted human populations for at least the last 13,500 years. These are the second largest springs in Texas and support a tremendous amount of wildlife. The San Marcos Springs are the headwaters of the San Marcos River, which in historic times provided power to gins and corn and grist mills. The mean annual flow of the San Marcos River is about 170 cubic feet per second. This measurement, however, is heavily dependent upon weather and climate; discharge rates for the springs is sure to have been different at various times in the past. The San Marcos Springs were an important stop on the Spanish El Camino Real (the "Royal Road"), a network of roads that linked interior Mexico with frontier regions of the Spanish Empire to the north. The springs were also a stop on the Chisholm Trail, which in its heyday (ca. AD 1867-1884) was used to drive five million cattle from as far south as the Rio Grande Valley to Kansas, where they were shipped to markets in the east via rail road.

    Purgatory Creek, a tributary of the San Marcos River, is immediately southeast of Zatopec. The creek's headwaters are at the western edge of Hays County and it flows approximately 20 miles southeast to its confluence with the San Marcos River, just beyond the city limits. This creek is dry today and only intermittently carries water during periods of heavy rainfall. However, it likely held at least a small stream in the past, making the landform where the site is located an attractive locale for seasonal habitation.

  • Another component of this transitional zone that Zatopec occupies is climate. To the east, Texas' climate is characterized as humid subtropical, and to the west it is semi-arid. In Hays County, based on a 30-year record, summers have mean maximum temperatures approaching 97 degrees Fahrenheit, and winters have mean minimum temperatures near 40 degrees Fahrenheit. December and January are the only two months in recorded history that have not had temperatures recorded above 90 degrees Fahrenheit, while freezing temperatures have been recorded in months between October and April. The mean annual precipitation recorded for Hays County is 33.75 inches; late spring and early fall are particularly rainy.

    Weather in Central Texas is dynamic and quickly changing. It is often dramatic and marked by severe events, and hazardous weather is not uncommon. The Hill Country is particularly vulnerable to flash floods due to thin soils and steep slopes. Cloud bursts may unload heavy precipitation on a confined area in a relatively short time, causing the area's tributaries and river levels to rise rapidly. Conversely, drought is also common to Central Texas. There is not a decade in the 20th century that did not experience drought conditions.

    As ancient conditions cannot be directly observed, however, they must be reconstructed using proxy measures; these are data that reveal different responses to climate and weather change in cases where climate can not be directly observed. Reconstructing paleoenvironments and paleoclimates (paleo = past) is an important contextual component of investigating prehistoric humans. Paleoenvironmental reconstructions help researchers understand the natural conditions that may have affected the availability of necessary resources (for example, water, food, and shelter) in addition to factors that may have potentially affected site preservation. Examples of proxy evidence for paleoclimate reconstructions include but are not limited to tree rings,  fossils, sediments and soils, speleothem growth (stalactities and stalagmites), phytolyths (durable structural portion of plants), stable isotopes (long-lasting species of elements), and faunal remains. Each proxy provides only a piece of the puzzle, and so as more lines of evidence (proxies) are used, more is understood about a paleoenvironment.

    For Zatopec, archaeologists relied on a number of previous investigations from Central Texas that used a variety of proxies including speleothem growth rates, phytoliths, stable carbon isotopes, alluvial (stream-origin) sediments, faunal remains, and treering growth (Palmer Drought Severity Index). Generally, the Late Pleistocene (more than 10,000 years ago) was cooler and wetter than today, supporting vegetation and animals suited to these conditions. After the Pleistocene, the Holocene (10,000 years ago to present) is characterized as becoming dryer and warmer through time, and it contains a peak in dryness during the middle of the period. Diminishing amounts of precipitation and cool temperatures through the Holocene caused different suites of plants and animals to migrate into and out of the region.


Bison image: George Catlin, 1832, "Buffalo Bull Grazing on Prairie," Smithsonian Institute
City of San Marcos Birds-Eye Map (top right): August Koch, 1881