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Iz potential and that colluvial sediments on the structure benches and the third terrace date from the • middle Holocene. However, this is a preliminary observation and absolute radiometric dating is needed to refine and document these propositions. Relatively weak soil development in the lowest elevation alluvial fill terrace (T1) and the presence of a buried paleosol suggests that it is a late Holocene landform similaz in age to the Tl fill terrace observed at Van Bremmer Arroyo (McFaul 1990; McFaul and Reider 1990; Schuldenrein 1985). Position, height above the modern drainage and compazatively stronger soil development suggest the T2 terrace dates from the late Pleistocene-earliest Holocene. The shallowness of soil above bedrock, its weak development, and the presence of a stone line at the bedrock contact. suggests the T3 surface was erosionally stripped and that it will not yield cultural materials dating older than the middle Holocene. Soils are comparatively thin on the high- elevation structural benches, however, in swales a soil profile is present that is much like the TI profile. Like the T1, it is suggested these sediments have the potential to yield cultural materials dating to the middle Holocene. Petroeranhic Analysis Several samples of stone from SLA6981 were sent to Jim Miller for petrographic analysis. SLA6981 is a primary tool stone source and is the only known systematically exploited quarry on the project area. The tool stone makes up the vast majority of lithic debitage in all the sites found during the project, and, based on descriptions from other nearby projects, was used up and down the Purgatoire River. • The stone quarried at SLA698] is a quartz keratophyre, a type of felsite. It is the aphanitic equivalent of alkali granite and very similar to rhyolite. It occurs as near surface sills, dikes and volcanic necks, and does not exhibit a regular stratigraphic association. The exposure at SLA6981 is probably a volcanic neck or similaz feature. Other exposures of the material were noted on the project area, but this site is the only exposure found where the material was knappable. Debitage, hammerstones, and bifaces of various stages are extremely common on the site. Debitage counts are estimated in the tens of thousands. No quarry features were found; it appears that materials were collected directly from the surface and from several outcrops that occur on the site. The felsite is composed of alkali (potassium) feldspar (ca. 70%), quartz (ca. 17%), sodic plagioclase (ca. 5%), and various micas (ca. 8%). On fresh breaks, the rock is a dark pinkish gray, but surface weathering alters the various minerals causing the stone to form a lighter patina with occasional dark brown flecks of ferrihydrite from alteration of the mica. On the oldest weathered surfaces, the mica is removed completely, leaving a texture superficially resembling siltstone. The ground mass of the stone consists of euhedral to anhedral crystals rarely larger than 0.01 to 0.001 µm. Phenocrysts are euhedral and about 1.0 µm in size. There is no observable mineralogical difference between the ground mass and phenocrysts. The presence of distinguishable phenocrysts in asmaller-grained ground mass, lacking mineralogical distinction, suggests a two stage intrusion. Miller suggests that it may be possible to isolate sources of this material based on ground mass and phenocryst size, which reflects the history of intrusion, or, • more significantly, using some form of trace element analysis.