Early dates of human occupation in the Western Hemisphere using the Calico archaeological site in southern California as an example

Kristine Bryan

Uranium-series and soil-geomorphic dating of the Calico archaeological site, California. James L. Bischoff, Roy J. Shlemon, T.L. Ku, Ruth D. Simpson, Robert J. Rosenbauer, Fred E. Budinger, Jr.

This paper attempts to validate very old dates calculated for the controversial Calico archaeological site in southern California. There are two different dating methods employed to accomplish this. Geomorphic correlation of soil strata was used to support dates confirmed by Th230 ­ U234 dating. This site is located in an arid region of southern California with a history of semi-arid/arid surfical deposition throughout the Pleistocene and Holocene. The site itself is located within an alluvial fan and consists of large groupings of lithic tools. Geomorphic correlation of the artifact bearing deposit lead the authors to an age between 150,000 and 200,000 yr. old. U ­ Th dating is based on a technique previously developed by Ku and others (see following paper summary). Bischoff and others calculated the age of artifact bearing deposits to be between 193,000 and 260,000 yr. old using this method.

The fundamental weakness in their argument is that the deposits are found on an alluvial fan which is unstable. It may be that there was more movement of artifacts after deposition than the authors are accounting for.

Th230 ­ U234 dating of pedogenic carbonates in gravelly desert soils of Vidal Valley, southeastern California. Teh-Lung Ku, William B. Bull, S. Thomas Freeman, Devin G. Knauss

This paper describers the technique of Th230 - U234 dating on carbonate deposits in soil near the Calico Archaeological Site. The surficial deposits were developed in this region during the Pleistocene and Holocene in both semiarid and arid climates. This paper focuses on 14 carbonate samples taken from "Q2b" geomorphologic surfaces which are recognized as Quaternary in age throughout Arizona and California based on previous research. These surfaces are thought to be Late Pleistocene in age. One can estimate the age of the soil from which the carbonate was taken through the process of counting Th230, U234 and U238 ions and then applying these values to the following formula:

Th230 = U238[1 - exp(-l0t)] + (U234 ­ U238)[l0/(l0 - l4)][ 1 ­ expl4t - l0t)]

where l0 = decay constant of Th230 (9.22 X 10-6 yr-1)

t = age of the carbonate sample

l4 = decay constant of U234 (2.79 X 10-6 yr-1).

The carbonate used for dating was developed through a process of illuviation. Pebbles with intact carbonate coatings (no "salt-splitting") were gathered from the field. The inner 203 mm of carbonate were extracted, processed, and then U and Th ions were counted in a mass-spectrometer. They had to correct for the fact that some U or Th is contaminated the sample from detrital material; i.e. the system was not "closed." Basically, they subtracted from the amount of Th230, U234 and U238 correction formulas based on the ratio of Th230/Th232 in the residue, the ratio of weight fraction of residue/weight fraction of leachate, as well as the difference between the amount of Th230, U234 and U238. The mean age of all 14 samples is 83,000 yrs ± 10,000 yrs BP. The accumulation rate is about 0.5 mm per 10,000 yrs of arid climate. They emphasize the importance of evaluating "contamination" from other noncarbonate sources. They determined minimum dates from other Holocene and Pleistocene surfaces. These minimum surface ages range from 10,000 for a Holocene surface up to 320,000 yrs BP. They find that this "background noise" of U and Th concentrations average about 4 ppm and they believe it is from clay based fraction.

I found this paper and well organized but still hard to follow. It seems to me that some points would have been stronger if they included a more thorough introduction.

The Calico Early Man Site. Fred E. Budinger, Jr.

This paper summarizes the lithic artifacts found at the Calico archaeological site in California. Approximately 11,500 stone tools were retrieved from this site between 1958 when the site was discovered and 1983 when this paper was written. The types of tools recovered include but are not limited to scrapers, cutting tools, boring tools, choppers, as well as a few bifacial tools. Budinger lists approximately a dozen concise criteria to validate these items as stone tools. Examples of these criteria include but are not limited to 1) the artifacts were located in distinct groups, 2) the artifacts demonstrate purposeful flaking or formation, 3) some artifacts show evidence that they underwent retouching. Budinger then reviews results from the correlative dating procedure employed by Bischoff and others (see first paper summary) as well as some other research. Budinger concludes this section by reiterating that the lowest artifact-bearing deposits at the Calico Site are at least 200,000 years old.

It seems+ that this paper was a relatively thorough summary of the lithic technology of the site and did a good job in this review.

Lithic Technology of the Calico Mountains Site, Southern California. Ruth D. Simpson, Leland W. Patterson, Clay A. Singer

This paper provides another summary of the lithic technology found at the Calico archaeological site as well as introducing issues contributing to the controversial nature of this site. The soil excavated from 3" layers is screened through customary _", _", and 1/8" screens from approximately 10 to 26 feet in depth. The presence of lithics such as unifacial tools demonstrate that these stone implements are indeed man-made as it is nearly impossible for forces of nature, such as a mud flow, to preferentially flake stone on only one side. Other detailed investigations of the stone tools reveal distinct workshop clustering of artifacts and that edge-wear of some of the artifacts is consistent with chopping use.

This paper is a less objective format than a standard scientific paper. It is part of a collection of papers in a publication by The Center for the Study of Early Man specifically challenging the current theory on the earliest dates of North American human occupation, which most feel is about 15,000 years ago.

The Calico Mountains Archaeological Project: A Progress Report. Ruth Dee Simpson.

This paper published in 1982 presents a field-season by field-season account of the Calico archaeological site. A visit to the site by Dr. Louis Leakey is also described. At the time of this writing, there had been more than 3500 stone tools and 6000 flakes recovered from the site. Steady excavation of the site continued after Dr. Leakey's initial visit in 1963 up until his death in 1972 during which time he seemed to have a significant influence on how the site was excavated. After 1972, funding was not dependable and volunteers were employed to continue the excavation. Simpson proceeds to briefly list which researchers and their specialties involved in the project. At the time of this writing, the most dependable date calculated for this site is about 60,000.

This paper is another subjectively written summary of the Calico Site. Simpson was deeply influenced by Dr. Leakey and it seems apparent in her written that she modeled her opinion of the site after Leakey's. It also provides interesting insight into the history of archaeological excavation at this site.

Artifacts or Geofacts at Calico: Application of the Barnes Test. Louis A. Payen

This paper challenges the validity of the Calico archaeological site by applying a statistical test to the lithic tools recovered from the site called the Barnes Test. The Barnes Test, developed in 1939, presumes that naturally occurring percussion flakes have an angle between the bulb of percussion and the striking platform greater 90o. Conversely, those flakes which are considered human-made have an angle less than 90o. Because this theory was meet with criticism, part of the purpose of this paper is to duplicate the Barnes Test before using the data from the Calico site to confirm the validity of the Barnes Test.

14,000 measurements were made on 54 collections of known controlled and uncontrolled fracturing. The results demonstrate that the Barnes test is statistically valid and therefore can be used on the Calico site artifacts. After application of the test on the Calico site artifacts, it is apparent that they are not artifacts.

This paper seems to have presented valid counter-evidence to the Calico archaeological site.