Rock Painting Depicting Re-Incursion of Bison onto the South Texas Plains: Painted Indian Cave, Pedernales River, Blanco County, Texas
Brock, Emily, Hixson, Charles, Guilderson, Tom, Murr, Priscilla, Rowe, Marvin W., Plains Anthropologist
We extracted carbon from a sample removed from a small, non-descript, solid monochrome pictograph at Painted Indian Cave site on the Pedernales River, Blanco County, Texas (41BC1). It contains red iron oxide pigment and is approximately 10-20 cm in size. The sample was taken with a surgical scalpel with a new blade. Plasma-chemistry was utilized to extract the organic carbon, without getting contamination from inorganic carbon-bearing minerals, calcite and calcium oxalate. Because the background of organic carbon in nearby unpainted rock (limestone) was negligible, the age should be reliable. Further, it is supported by archaeological inference. However, as always with only a single radiocarbon date, especially with minimal carbon extracted, caution is advised pending further study. Radiocarbon analysis at the Center for Accelerator Mass Spectrometry of the Lawrence Livermore National Laboratory indicated an age of 770 ± 50 years BP. The age is consistent with the image of a bison within the small cave. The depiction of the bison probably corresponds with the earliest Late Prehistoric sightings of bison as they re-entered the south Plains of Texas in larger numbers.
Keywords: rock painting; plasma-chemical extraction; radiocarbon dating; Late Prehistoric bison; central Texas Plains
The advent of accelerator mass spectrometry (AMS) as a tool for measuring radiocarbon greatly reduced the amount of carbon necessary for analysis (Bennett et al. 1977; Muller 1977; Nelson et al. 1977) so that we can often get reliable dates even on the extremely small amounts of carbon that can be extracted from rock paintings (e.g., Jensen et al. 2004; Rowe 2001,2004 and references therein from the Texas A&M University laboratory; Russ et al. 1990; Scott et al. 2005; Steelman et al. 2004, 2005).
On the north bank of the Pedemales River in Blanco County of central Texas, there is a small limestone cave (41BC1 ) called Painted Indian Cave that contains at least ten separate pictographic images. The paintings are faded red monochrome that utilize iron oxide (ocher) as pigment. The site is unusual in two ways: (1) no other rock paintings or petroglyphs are recorded in that county and (2) the depiction of a bison there. The paintings are all in red ocher and are about 25 cm or less in size. Depicted are, among other images, a bison (shown in Figure 1), three anthropomorphic figures (one of which is illustrated in Figure 2), and geometric designs (one panel of which is shown in Figure 3), as well as nondescript painted areas, one of which was sampled and dated here. All the paintings appear to be made from the same, or very similar, paint and were probably painted over a short span of time.
The cave is a single roughly circular chamber about 9 m in diameter and about 2 m high in the center. One can access the cave by either of two entrances. A meter or so to the west of the larger entrance, which is on the south side facing the river, the second entrance is a crevice about 2 m high. The floor slopes up towards the rear of the cave where it meets the sharply rising back wall. There are no archaeological deposits in the cave.
No firm inference could be made a priori about the age of the paintings at 41BC1, except that they are relatively recent. The first clue, the fact that the cave is sometimes flooded by the Pedernales River, in itself argues against great antiquity; one would simply not expect pictographs to survive for millennia. Based on that fact alone, Turpin surmised that the pictographs there were probably Late Prehistoric to Historic in age (Solveig A. Turpin, personal communication 2004). Furthermore, Ron Ralph (2002) in his State Report, listed the time period of occupation as "perhaps Late Historic". Because the cave has no obviously Historic-age paintings, i.e., horses, churches, etc., Late Prehistoric is preferred here. In addition, the iconography suggested to Turpin that the paintings were not older than Late Prehistoric (Solveig A. …