Friday, June 25, 2010

A New Nevada Obsidian Source: Robinson Summit

This source blended so well into the background that it was only today that we realized that it even existed.  Daron Duke (Far Western Anthropological Research Group) recently sent us a couple of obsidian source nodules that he had found during a survey not far east of Jakes Valley near Robinson Summit.  Daron mentioned that the obsidian was rarely found in the alluvial deposits leading westwards from the Robinson Summit area down into Jakes Valley.  Subsequent XRF analysis this morning indicates that it's a brand new source that we didn't even realize we were missing!  The trace element composition is very similar to that of the Montezuma Range source (strontium levels are a bit more elevated) located near Tonopah and the two sources could be easily confused.  A search of the lab database revealed only a single possible artifact match for the Robinson Summit source, an item that had been misassigned as Montezuma Range during the analysis of a large number of artifacts from Butte Valley (located just east of Jakes Valley).  Once again, luck proves to be one of our most effective analytical tools.

Tuesday, June 22, 2010

Top 10 Obsidian Sources: California

With nearly 22,000 characterized artifacts in the lab database, the number of California obsidian artifacts in an individual state is exceeded only by Oregon.  The top 10 favorite prehistoric sources are:

1.  Medicine Lake (all varieties)
2.  Coso Volcanic Field (all four varieties)
3.  Napa Valley (North Coast Ranges)
4.  Bodie Hills
5.  Casa Diablo (Lookout Mountain and Sawmill Ridge varieties)
6.  Tuscan (all varieties)
7.  Queen
8.  Buck Mountain (Warner Mountains)
9.  Saline Valley (all three varieties)
10.  Borax Lake (North Coast Ranges)

Sources 1 through 6 all had in excess of 1000 characterized artifacts each.  I lumped together the different source varieties for some of the source areas - Medicine Lake, Coso, Casa Diablo, and Saline Valley - because some early provenance studies didn't distinguish among the different subsources that were eventually identified.
Tall Tales from the End Of the Trail 2
The second story from Oregon: End of the Trail comes from page 470 as part of another auto tour. For many years, there was a persistent rumor that obsidian from Glass Buttes made its way to the Hopewell mounds of Ohio, a truly spectacular example of long-distance trade in the North America.
In the section above, the writers spin an excellent yarn and can be commended for their imagination if not their attention to the facts. There's no doubt that Glass Buttes in one of the premier sources of natural glass in the United State, if not the world - obsidian has been historically collected in this area for many years and the hillsides are pocked with holes, some of them big enough to drive large vehicles into. And it's true that a surprising number of obsidian artifacts have been recovered in the Midwest in association with Hopewell period sites - their source was the subject of considerable speculation prior to their geochemical characterization in the late 1960's.
But once again the facts spoil what was a good story. It turns out that the source of the Hopewell obsidian was located in Yellowstone National Park (Obsidian Cliff) and in eastern Idaho not far from Yellowstone (Bear Gulch). Trace element studies of obsidian artifacts from Glass Buttes demonstrate that this source was used in central and eastern Oregon, Washington, and even British Columbia, but that the glass definitely didn't make its way east to Ohio. In fact, we've never seen a Glass Buttes artifact in any of the neighboring states to the south or east - California, Nevada, and Idaho.
Tall Tales from the End of the Trail 1

The American Guide Series was a collection of books published by the Federal Writer's Project during the late 1930's and early 1940's. Among the publications was Oregon: End of the Trail, a description of the state along with a collection of auto tours. Although the book offers a fascinating snapshot of a Depression-era Oregon, it also proved to be the source of a couple of obsidian-related whoppers. The book appears to be well-researched but it's clear that the writers played it pretty loose on occasion with the facts.

The first of these concerned Rock Mesa, a 2000 year-old obsidian flow located at the southern base of the South Sister. While the flow is quite spectacular, the quality of the obsidian is pretty poor and the source received little or no attention as a prehistoric toolstone resource. The Writer's Project book, however, spins a very different tale in Tour 4B:

The authors paint a fascinating picture of territoriality and quarry control and ultra long-distance trade but unfortunately their interpretation has absolutely no basis in fact. Subsequent trace element provenance studies of thousands of artifacts from western and central Oregon indicate that Rock Mesa was seldom, if ever, used as a source of obsidian. Great story though!

See the next entry for tale #2, a somewhat more plausible but perhaps even taller tale.

Wednesday, June 16, 2010

Top 5 Obsidian Sources: Colorado

1. Polvadera Peak (NM)
2. Cerro del Medio (NM)
3. Malad (ID)
4. Obsidian Ridge (NM)
5. Cochetopa Dome

Like Washington, Colorado suffers from a severe shortage of good quality prehistoric obsidian sources and four of the five top sources are located in other states - New Mexico (Jemez Mountains) and Idaho. Polvadera Peak is the clear winner on the list and over 50 precent of the analyzed artifacts from the entire state are from that source. Over three-fourths of all characterized Colorado artifacts originated from sources in the Jemez Mountains of northern New Mexico.

We only have a little over 400 Colorado obsidian artifacts in the lab database but it appears that the choice of source is strongly influenced by the geographic location of the site or artifact. For more on this, see the article below by Ferguson and Skinner (2003).

Ferguson, Jeffrey R. and Craig E. Skinner (2003) Colorado Obsidian? Preliminary Results of a Statewide Database of Trace Element Analysis. Kiva 69(4):35-50.
Top 5 Obsidian Sources: Washington

1. Inman Creek (OR - combined A and B varieties)
2. Obsidian Cliffs (OR)
3. Newberry Volcano (OR)
4. Elk Pass
5. Whitewater Ridge (OR)

Washington suffers from a shortage of artifact-quality obsidian sources and it's no surprise that four of the five top sources represented among Washington artifacts are located in Oregon. The only indigenous source that made the list was Elk Pass, a High Cascades source whose prehistoric use was largely relatively local. No artifact from this source has yet been found to the south in Oregon.

The total number of characterized Washington artifacts numbers about 1,500 and all of the top 5 sources contained at least 100 analyzed artifacts.

Tuesday, June 15, 2010

Top 10 Obsidian Sources: Oregon
1. Newberry Volcano
2. Obsidian Cliffs
3. Whitewater Ridge
4. Silver Lake/Sycan Marsh
5. Inman Creek (both A and B varieties)
6. Spodue Mountain
7. Quartz Mountain
8. McKay Butte
9. Glass Buttes Source Complex (all nine geochemical varieties)
10. Medicine Lake Highlands Sources (CA - GF/LIW/RS and East Medicine Lake)

With over 100 geochemical obsidian sources, some of them spread over large geographic areas, Oregon has been hands-down the toughest of the U.S. states to untangle. But with over 30,000 characterized artifacts and over 5,000 analyzed source samples, it's also one of the most thoroughly studied. All of the top 10 sources in Oregon were represented by at least 1,000 artifacts.
Top 10 Obsidian Sources: Utah

1. Wild Horse Canyon
2. Topaz Mountain
3. Black Rock Area
4. Modena
5. Browns Bench (UT, NV, and ID)
6. Malad (ID)
7. Pumice Hole Mine
8. Ferguson Wash
9. Kane Springs (NV)
10. Black Mountain

Among these 10, sources 1-6 make up the large majority of sources that are represented among our database of well over 8,000 characterized Utah artifacts.
Top 5 and Top 10 Prehistoric Obsidian Source Lists
We've started compiling state-by-state lists of top 10 or top 5 obsidian sources for most of the western United States and will be adding states here on a regular basis. Please note that these are casual compilations based on thorough queries of the laboratory database and are subject to all kinds of biases. In Oregon, for example, the majority of provenance studies have been carried out in the western half of the state and eastern sources are bound to be underrepresented. Large projects associated with gas pipelines or power transmission line corridors will also add plenty of bias to the results. That said, these lists should provide a overall sense of the major obsidian sources that were used by the prehistoric inhabitants of each state.