GWYNN AND EWE CANYONS

WESTERN NEW MEXICO

Sections 19,30,31,32 R16W, T9S USGS Telephone Canyon 7.5' Quad; Sections 30,31,32 R16W T9S; Secs. 4.5.9 R16W, T10S USGS Negrito Mtn 7.5' Quad (and see below), Gila National Forest, south central Catron County, New Mexico.

The Gwynn Canyon source was not personally surveyed during the original study. The information and samples used here was provided by Chris Stevenson (then) of New Mexico State University's Obsidian Hydration Laboratory (see also Hughes 1988a). The specimens for this study were all procured in Ewe Canyon south of another source area above in the Gwynn Canyon area (discovered first). The nodules (at least 5 cm in diameter) are found mainly in a volcanic alluvium and within the washes. The glass is a higher quality material than Mule Creek (not as brittle), but only 15 nodules were available for study. No specific reduction areas were noted by Stevenson, but most nodules were picked up in the canyon bottom. The 15 nodules studied all have waterworn black cortex and the aphyric glass ranges from an opaque black to a nearly transparent brown. Banding did not occur in this small sample.

There are no known published references on this new source other than the regional geologic map (Weber and Willard 1959).

[updated 1995] In the earlier study (Shackley 1988a), this source was not personally mapped or surveyed. My survey in 1993 indicated that marekenites were directly associated with glassy, perlitic rhyolite in Ewe Canyon to the south, although this stream system erodes into Gwynn Canyon. These coalesced domes shown as Feathery Hill on the quadrangle map, exhibit nodule densities in the regolith up to 200 per m². This source is located in Sections 19 and 20 T9S R16W Telephone Canyon 7.5' Quad 1963, Catron County, New Mexico. Unmodified marekenites on the domes have maximum diameters near 50 mm, although the vast majority (95%) are 30 mm and smaller. Bipolar cores and flakes were found on and near Feathery Hill, but in low densities (<1 per 100 m²).

As noted above, marekenites are eroding into the Gwynn Canyon system and possibly the upper San Francisco River, although no nodules were noted in the San Francisco River alluvium as far north as Alma, New Mexico. Published references for the geology of this source include Findlow and Bolognese (1982:56), the regional geology map by Weber and Willard (1959), and Ratté et al. (1984).

The Gwynn Canyon and two of the Mule Creek groups (Antelope Creek and Mule Mountains) are very similar in trace element composition. Zirconium plotted against Nb, Y, and/or Ba is the best method to discriminate these sources using EDXRF. This can be an important issue in western New Mexico late prehistory because these sources are located in very different environments that may have had cultural significance in prehistory. It is possible that in the late period Gwynn Canyon obsidian could have been controlled by the Cibola branch of the Mogollon while the Mule Creek sources could have been controlled by the Mimbres branch. This may or may not influence the spatial distribution of these obsidian sources in the region and confident source assignment can become crucial. Again, the secondary distribution of Mule Creek is quite extensive to the west through the San Francisco and Gila River systems, and the presence of Mule Creek glass in archaeological contexts to the west may not necessarily indicate that it was procured in the highlands, but could have been procured from the Gila River alluvium.

Elemental concentrations for Gwynn Canyon source standards. Samples 11-20 from Feathery Hill at the head of Ewe Canyon. All measurements in parts per million (ppm)

Sr, Rb, and Zr concentration plot of the Gwynn Canyon and Mule Creek sources. Note the possible genetic similarity.

This page maintained by Steve Shackley (shackley@berkeley.edu).
Copyright © 2001 M. Steven Shackley. All rights reserved.
Revised: 19 July 2006

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