Leslie L. Bush
Last fall, an archeologist working at TARL recognized a rare opportunity to look for plant remains from a site that had been excavated nearly 80 years ago. The site is the Rob Roy Site (41TV41), located in western Travis County, Texas on a terrace of the Colorado River. Austin residents will recognize the name for the residential subdivision that now overlooks the site. University of Texas personnel led by Dr. Kalvero Oberg excavated at Rob Roy from December 1938 to April 1939 with funding from the Works Progress Administration (WPA). Artifacts and notes were sent to TARL, but as attention turned toward World War II, the materials were never properly analyzed or written up.
Regular readers of the TARL blog know that retired archeologist Dan Prikryl is currently working on the Rob Roy collections (December 2016, December 2017). He originally planned to use two charcoal samples from Rob Roy for radiocarbon dating, but he quickly realized that the soil collected along with the wood charcoal could contain small seeds or bulbs from foods and other useful plants. These could be parts of food plants that were accidentally burned during cooking, medicinal plants discarded after being used in poultices or teas, or debris from plants used for objects like baskets that were disposed of by burning in a campfire. Only plants that have been carbonized (turned to charcoal in a fire) can survive in the soil for hundreds or thousands of years at a site like Rob Roy where the deposits aren’t protected by cave walls and where the climate is humid enough that fresh plant parts decay into compost within weeks, months, or decades.
It’s not quite clear why Dr. Oberg directed workers to save charcoal samples from the Rob Roy site. WPA-era excavators working on large mound centers like the George C. Davis Site collected burned corn cobs and beans but not usually wood charcoal. Radiocarbon dating, which is often done on wood charcoal, hadn’t been invented in the late 1930s when excavations were going on. The principle of flotation processing, the method for extracting small seeds from archaeological soils, was known but didn’t come into common use in archeology until the 1980s. It’s possible Dr. Oberg knew about early studies in dendrochronology and dendroclimatology and decided to collect samples in case they turned out to be useful for tree ring dating or understanding past climate and weather patterns.
Since I specialize in identifying wood, nutshell, seeds, and similar plant material from archeological sites, Dan showed me the two charcoal samples from Rob Roy in the spring of 2017. I was able to select and identify a few fragments of wood charcoal for radiocarbon dating. Even in that quick scan, I could see that two types of wood had been burned in Feature 1, live oak (Quercus fusiformis; Figure 1) and an oak of the white group (Quercus sect. Quercus, which includes post oak, Q. stellata). Feature 2 contained white group oak, but it wasn’t clear if any other kind of plant material was present.
Figure 1: A fragment of live oak wood charcoal from Feature 1.
The size of the sample from Feature 1 was 4.1 cubic decimeters, about a gallon, and it included loose soil as well as charcoal. At 0.1 cubic decimeters, the sample from Feature 2 was smaller, roughly ½ cup, but it also included some soil. Dan and I judged that flotation processing would allow us to recover small seeds or bulb fragments that might be present but not readily recognizable among all the dirt and wood charcoal. Dan was interested in knowing what kinds of foods might have been cooked in the earth ovens at Rob Roy. Bison was abundant at the site, but plant foods are commonly cooked in earth ovens, too (Thoms et al. 2018). Many bulbs, roots, and tubers are more palatable and nutritious after the long slow cooking that earth ovens provide (Wandsnider 1997). In central Texas, these include wild onions and garlic (Allium spp.), eastern camas (Camassia scilloides), and scurfpea (Pediomelum spp.). We also hoped to recover plant material such as grass stems, grape leaves (Vitis spp.), and pricklypear pads (Opuntia spp.) that would have been used to provide moisture and insulate the food plants from the ash and charcoal in the fire. Dr. Steve Black, another archeologist associated with TARL (TBH co-editor) who has worked extensively on earth ovens, was also interested in seeing what, if any, plants might have been cooked in the earth ovens at Rob Roy. He provided a small grant to get the project underway.
TARL curator Marybeth Tomka prepared loan papers that allowed me to take the charcoal samples to my laboratory for processing and microscopic examination. Flotation processing is a water separation method where soil from an archeological site is placed in water to allow any bits of plants to float to the surface while soil particles and any artifacts sink to the bottom of the container. Floating plant material can then be poured off (decanted) into a fine mesh or scooped off with a fine mesh strainer. Flotation processing can be as simple as placing soil in a 5-gallon bucket and decanting plant material into the kind of fine mesh used in tent windows (Figure 2). Any heavier artifacts still in the soil can be separated by pouring the remaining sludge through a screen. This method is what I used for the Rob Roy samples. More elaborate flotation systems use devices like electric sump pumps, jet nozzles, and aerators to make flotation faster and easier. All three editions of Deborah Pearsall’s essential textbook, Paleoethnobotany, include extensive discussion of various flotation devices.
Figure 2: Flotation light fraction from the Eagle Bluff Site (41ME147), where light gastropods were decanted from the water surface along with modern rootlets and ancient charcoal. “24” is the number of this sample in the flotation log book.
Microscopic examination of the flotation samples showed that the archeological plants at Rob Roy consisted mostly of wood charcoal. Based on a sample of twenty fragments selected at random from each feature, Feature 1 contained about 85% live oak and 15% white oak. Feature 2 was at least 95% white oak, but a single fragment of wood charcoal was clearly not oak. The fragment was too small and brittle to identify conclusively, but the closest match appears to be povertyweed (Baccharis spp.), a weedy shrub that colonizes open areas near streambanks. Use of oaks for earth oven cooking makes a lot of sense both because they would have been common in the area even thousands of years ago and because they are dense woods that produce hot, long-lasting coals (Collier and Turner 1981; Marcouiller and Anderson n.d.). Carbonized fungi and insect droppings (probably termite) identified under the microscope indicate that the oak wood had been dead for some time prior to burning (Figure 3). Fuelwood was probably collected from snags or fallen trees in the gallery forest along the Colorado River.
Figure 3: Carbonized fungus from Feature 1 at the Rob Roy Site
No evidence of bulbs or tubers that are commonly cooked in earth ovens or evidence of any material used to wrap foods during cooking was found in either sample. Feature 1 did produce seeds from one food plant and one medicinal plant, however.
The probable food plant remains consisted of three seeds and one seed fragment of goosefoot (Chenopodium spp.) (Figures 4 and 5). Seeds of goosefoot plants are edible, and two species, C. quinoa (yes, that quinoa!) and C. berlandieri, were domesticated for their edible seeds in ancient times by Native American Indians. At least four species of goosefoot grow in Central Texas today, including C. berlandieri (Figure 6). No evidence for domesticated C. berlandieri has been found in the area, and the seeds from Rob Roy have thick, wild-type seedcoats. Goosefoot, quinoa, and other chenopodium species are members of the spinach family, known for nutritious, iron-rich greens. Goosefoot greens as well as seeds may have been exploited by the ancient inhabitants of the Rob Roy Site. In addition, the flowering seedheads of chenopodium species are edible, raw or cooked, like modern broccoli (Glore 2006). Nutritional studies of various species of chenopodium show they can be important sources of protein, minerals (especially iron), anti-oxidants, and anti-microbials (Navruz-Varli and Sanlier 2016; Poonia and Upadhayay 2015).
Figure 4: Goosefoot (Chenopodium spp.) seeds and seed fragment from Feature 1, Rob Roy Site.
Figure 5: Chenopodium plants can be difficult to identify to species. This one, photographed in San Saba County on August 18, 2018, is either slim-leaf goosefoot (C. leptophyllum) or thick-leaf goosefoot (C. pratericola).
Figure 6: Fruits of pitseed goosefoot (Chenopodium berlandieri) from a wild stand in western Travis County, Texas.
The probable medicinal plant remains consisted of one seed and two seed fragments of pricklypoppy (Argemone spp.) (Figures 7 and 8). To the author’s knowledge, this is the first pricklypoppy recovered archeologically in central Texas, although it is known from the Tres Metates Site in the Trans-Pecos (Dering 2008). Among historic Native Americans, use of pricklypoppies was almost always medicinal, and seeds were typically the plant part used. Paiutes, Shoshones, Kawaiisu, and Washoes used a salve containing the crushed seeds for cuts, sores, and burns (Moerman 1998:89-90). Shoshones used the salve to kill lice as well. Shoshones and Comanches used an infusion of pricklypoppy seeds to treat sore eyes, and Shoshones also ate pulverized seeds as a more general medicine (Moerman 1998:89-90). An American native, pricklypoppy is now widespread in warm regions worldwide, and its seeds, leaves, and roots have been used by many people to treat ailments from toothaches and eye problems to cancer (Cheatham et al. 1995:448-458).
Figure 7: Pricklypoppy seed from Feature 1, Rob Roy Site
Figure 8: Prickypoppy (Argemone sp.) photographed in western Travis County, Texas.
Although it was disappointing not to find evidence of typical earth oven plants like camas bulbs, scurfpea tubers, or prickypear pads, the information gained by processing and examining the flotation samples is still useful. First, we discovered evidence that the ancient inhabitants at the Rob Roy site were using pricklypoppy, probably medicinally, and eating the leaves, seeds, and/or flowering seedheads of goosefoot. As to what was cooked in the earth ovens, the lack of bulbs, tubers, or packing material suggests either that the people at Rob Roy were such very careful cooks that no plant foods or packing material were accidentally charred or that the earth ovens were used to cook something other than plant foods. Given the abundance of bison bone at the site, pit cooking of bison is a strong possibility.
Insights from plant remains at the Rob Roy Site highlight the long-term research potential of the extensive WPA collections at TARL: eight decades on the shelf and still yielding new data!
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