COW CANYON

EASTERN ARIZONA

Since the original survey of this source in the mid-1980s, I've re-visited the primary domes and surveyed to the west toward Eagle Creek, and the east toward the Blue River multiple times.  As noted below, the primary highly eroded dome complex at the upper end of Cow Canyon is on a divide where some of the source obsidian erodes west into Eagle Creek and then into the Gila River, and some erodes east toward the Blue River, on into the San Francisco River, and then the Gila River (see map here; Shackley 2016).  The text below describes the evolution of the knowledge of the source from the mid-1980s until 2016.  The source was first noticed by Glen Rice (Arizona State University) while engaged in his Ph.D. dissertation fieldwork in the Blue River region.

From Shackley (1988, 1989). Sections 2 and 3 R29E, T2S, USGS Pipestem Mtn 7.5' Quad, Apache National Forest, central Greenlee County, Arizona. This is a relatively small source along and east of Arizona Hwy 666 [now 191] located in a Neogene rhyolite body. There is some suggestion that this too is a Tertiary rhyolite body remnant surrounded by the Quaternary basalt, but this was difficult to determine for this study. The nodules are found within an eroded rhyolite/ash unit that appears to be a remnant dome structure. Perlite or vitrophyre was not evident. The nodules are common in a rhyolite regolith on top of the dome as well as the rhyolite/ash alluvium at the base of the slopes. Nodules up to 5 cm in diameter are available, but most of the nodules are near or less than 4 cm. The density of nodules is fairly high in places, up to 5 per m². Cortex is mainly a thin gray-black often with a velvet-like character. The interior glass is aphyric and the color is as variable as many of the mid-Tertiary marekanite sources. The most common color/opacity is a near transparent brown-green sometimes with thin banding. A few specimens exhibit a nearly opaque aphyric gray-green banded megascopic character.  The nodules are eroding and funneled into the Cow Canyon Creek/Turkey Creek system possibly reaching the Blue River 15 km east. Reduced nodules and flakes occur everywhere on the regolith and in the alluvium. The pattern of reduction is similar to Vulture with sporadic bipolar reduction throughout the source area. Overall the rejected core/flake density is less than 1 per 5m². There are no published sources on this locality other than the county geology map (Wilson and Moore 1958).

[updated 1995] It appears that the secondary depositional extent of this source is much greater than originally mapped (Shackley 1988). This Tertiary source is eroding east into the Blue River, south into the San Francisco River and west into the Gila River as originally noted, but also erodes in much higher density west into Eagle Creek west of the Blue River, and on south into the Gila River and up to 20 km south into the San Simon River Valley. A number of “pockets” of Cow Canyon glass have been located in the San Simon River Valley in Pliocene/Pleistocene sediments the result of considerably higher sedimentation rates in these periods than currently. The density of nodules at Eagle Creek approximately 15 km west of the primary contexts at Cow Canyon is up to 1 per 10m², and less than 100 times lower in the Gila River (Shackley 1995). Again, these nodules are mixed with the Mule Creek marekanites in the alluvium.

The 111 Ranch Formation.  In the mid-1990s while conducting field schools in the San Simon River Valley, Pat Gilman (University of Oklahoma) identified some marekanites up to 50 mm in diameter eroding out of the 111 Ranch Formation, a Pliocene lacustrine sedimentary formation in the San Simon Valley (see map here).  These lacustrine sediments dating between 2.17 and 2.67 Ma were formed when the ancestral Gila River was dammed downstream and created a shallow lake in the basin, most recently mapped by Houser et al. (1985).  The sediments are often gypsiferous and marekanites often exhibit calcium carbonate on the exterior (see images here).  What is unique in the 111 Ranch Formation is that while the elemental concentrations overlap the Cow Canyon primary source and secondary deposits above Eagle Creek on Robinson Mesa upstream, the Sr and Ba concentrations are often a bit lower, and the nodule sizes are larger, up to 50 mm not seen in the Cow Canyon secondary deposit nodules in San Francisco and Gila River alluvium, although up to that size at the Cow Canyon dome complex (see images and map here).  It does appear that the "source" for the 111 Ranch marekanites is in the Robinson Mesa area above Eagle Creek upstream, and the event that created the lake in the basin was likely a very large fluvial event (see elemental analysis discussion below).  At the Murray Springs Clovis levels, all the obsidian artifacts including two Clovis points were produced from the higher Sr Cow Canyon obsidian, so the raw material was likely procured near or at the primary domes, although this is impossible to verify (Shackley 2008, see also Shackley 1989).

Compositional XRF Analysis, 2016.  In order to better understand the relationship between the Cow Canyon Dome Complex obsidian and that recovered from the 111 Ranch Formation the original mid-1980s samples, samples collected in the 1990s, and the 111 Ranch Formation samples collected in the 1990s were analyzed or re-analyzed (see accompanying tables and plots).  As mentioned above, while the 111 Ranch Formation obsidian generally exhibits lower Sr and Ba concentrations, there is considerable overlap between 111 Ranch and the primary domes and particularly the secondary deposit obsidian on Robinson Mesa and along Eagle Creek, west of the primary domes (see data and plots here).  Given this, I suggest that the source(s) be called Cow Canyon or Cow Canyon/111 Ranch, the former would be most correct since it does appear that the origin is upstream somewhere in the Cow Canyon to Robinson Mesa area.

Digital elevation model of the location of the collection localities analyzed including the Cow Canyon Dome Complex and the 111 Ranch Formation.

Mean and central tendency for the Cow Canyon source standard elemental concentrations.

Elemental concentrations for the source standards by locality and USGS RGM-1 rhyolite standard.

              

Ba/Zr and Sr/Rb bivariate plots of the Cow Canyon source standards by locality.  Note slightly lower Sr in the 111 Ranch samples, but elemental overlap between all localities. Confidence ellipses at 95%.

References Cited 

Houser, B.B., D.H. Richter, and M. Shafiqullah, 1985, Geologic map of the Safford Quadrangle, Graham County, Arizona.  USGS Miscellaneous Investigation Series Map 1-1617.   

Shackley, M.S., 1988, Sources of archaeological obsidian in the Southwest: an archaeological, petrological, and geochemical Study.  American Antiquity 53:752-772. 

Shackley, M.S., 1989, Early hunter-gatherer procurement ranges in the Southwest: evidence from obsidian geochemistry and lithic technology. Ph.D. dissertation, Department of Anthropology, Arizona State University. 

Shackley, M.S., 1995, Sources of archaeological obsidian in the greater American Southwest: an update and quantitative analysis.  American Antiquity 60:531-551. 

Shackley, M.S., 2008, Source provenance of obsidian artifacts from the Murray Springs Clovis     Site, southern Arizona.  Report prepared for C. Vance Haynes, Department of Anthropology, University of Arizona. 

Wilson, E.D., and R.T. Moore, 1958  Geologic map of Graham and Greenlee Counties, Arizona. Arizona Bureau of Mines, University of Arizona.

This page maintained by Steve Shackley ([email protected]).
Copyright © 2016 M. Steven Shackley. All rights reserved.
Revised: 14 January 2019

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