VULTURE

WESTERN ARIZONA

From fieldwork October 2008:

In October 2008 with NSF funding, the Vulture area was re-visited in an attempt to locate the primary domes and better elucidate the extent and character of this source that is so prominent in Sacaton Phase Hohokam sites in the Lower Salt River Valley to the east (Shackley 2005).

This Tertiary Period source appears to be derived from earlier rhyolite eruptive events that are now part of and mostly subsumed by the andesitic Vulture and Diamond Mountains of northwestern Maricopa County, Arizona (see images below).  Obsidian marekanites, similar to the 1985 study are common in the alluvium and regolith along and above Jackrabbit and Coyote Washes in the region.  Located in this study were marekanites embedded in ancient ash flow tuffs, perlite, and possible lahars along Jackrabbit Wash just south of the Vulture Mountains.  Most often the marekanites are found in the ashy regolith that often overlies the tuffs and perlite they have been eroding from the rhyolite domes since the Tertiary.  In a few exposures, marekanites were seen in-situ in the tuffs and perlite (see image below).  The first three samples analyzed in the table below were removed from the tuffs in the image below.  The elemental chemistry is identical to those marekanites recovered from the alluvium in the region in 1985.  So, the primary source for Vulture appears to be some Tertiary rhyolite events that have now been subsumed by later andesite volcanism.  The Vulture marekanites are remnants eroding from the ash flows and perlite from what appears to have been an extensive series of eruptions "flowing" to the southeast toward what is now the Gila River.  Near the "primary" source, marekanite densities are somewhat higher than that seen southeast in 1985 reaching 5-10/m2 (see below).  All of the 1985 observations seem still relevant in 2008.  Bipolar cores and flakes are common on ridge tops, at times reaching 10/m2.  One small biface preform, possibly a Sacaton period point preform was located near Jackrabbit wash, rejected for some unknown reason.

 

 

 

 

 

Digital elevation model of the "primary" and secondary Vulture marekanites along Jackrabbit Wash

 

 

 

 

 

 

 

 

 

 

 

 

Jackrabbit Wash in center with highly eroded ash flows and perlite lava terraces in foreground and background.  View to the south with the Eagletail Mountains in background. Photo taken from the slopes of andesite volcanoes in above image.

 

 

 

 

 

 

 

 

 

 

 

Remnant ashflow tuff along Jackrabbit Wash with marekanites.

 

 

 

 

 

 

 

Close-up of marekanites (near hammer point and above rock hammer) in ashflow tuff above.

 

 

 

 

 

From Shackley (1988):

Sections 1,12 R8W, T5N; Sections 4,5,6,7,8, R7W, T5N USGS Aguila 15' Quad; and Sections 2,3,4,9,10,11,14,15,16, R7W, T5N USGS Vulture Mountains 15' Quad, northwest Maricopa County, Arizona. Previous to this study, the Vulture source was the only fully documented archaeological obsidian source in central Arizona (P. Brown 1982). The geology here is very similar to other mid-Tertiary sources in the region, especially Sauceda. A series of bedded ash-flow tuffs are punctuated with roughly circular rhyolite bodies and remnant domes that grade to perlite or vitrophyre toward the outer margins (P. Brown 1982:230). Surrounding the silicic volcanics is an alluvium that contains chunks of rhyolite and basalt as well as marekanites up to 10 cm in diameter. The nodules are found at least 20 km south and east into the Hassayampa Plain and perhaps into the Gila River system. Nodule densities near the perlite-vitrophyre are fairly low (<10 per 5m2), but the area is a known "Apache Tear" locality for local rockhounds (Simpson and Mitchell 1989).

The nodules exhibit velvet-like to water eroded thin black cortex. The aphyric glass ranges from a nearly opaque brown-green to nearly transparent. Some nodules are banded or cloudy, and one specimen was evenly banded with greenish and black bands. The nodules are an excellent medium for small biface production.

Much of this source falls within a large lithic (obsidian, rhyolite, chalcedony) procurement site AZ T:5:5(ASU) (Brown and Stone 1982). Here, as at all the marekanite sources, sporadic occurrences of bipolar reduction stations are common. The presence of cores and debitage is also sporadic, probably corresponding to the prehistoric location of nodules. Small areas, usually less than 1m2, exhibit 15 to 20 rejected flakes, angular debris, and bipolar core fragments. These bipolar reduction areas may be 5 to 50 meters apart. Brown and Stone's study indicated that only 10% of the artifacts were utilized (1982:82). The vast majority of the recovered materials were unused flakes (Brown and Stone 1982:82). This suggests that the nodules were 'test knapped' and those found suitable were removed. This pattern of bipolar test knapping and removal of desirable flakes and cores is common on all the middle to late Tertiary marekanite sources. The lack of utilized artifacts is also a common pattern. The main published work on this source is P. Brown's (1982) study, as well as Wilson et al. (1957).

The two sources in central Arizona that are most frequently recovered in Arizona sites are Superior and Vulture. It is crucial to discriminate these sources, particularly in sites dating to the Sedentary (Sacaton) Period Hohokam where Superior is dominant in sites along the Middle Gila River, such as Snaketown and Grewe, while Vulture is dominant in sites along the Lower Salt River, and deviations from this pattern point to exchange likely through the market system employed through the ball games (Shackley 2005).  The two sources can be discriminated using Rb, Sr, Zr, and Ba.  The best discrimination is through plotting using the elements Zr and Ba (see below).

Ba versus Zr bivariate plot of Superior (Picketpost Mountain) and Vulture source standards

 

Raw elemental concentrations for Vulture source standards. All measurements in parts per million.  Samples beginning with "102308 or 102408" collected in October 2008.  The others collected in 1985 and data reported in Shackley (1995).

Sample Ti Mn Fe Zn Rb Sr Y Zr Nb Ba
102308-1-1 1061 410 7819 46 140 41 19 135 18 476
102308-1-2 1083 394 7707 52 131 37 21 134 22 472
102308-1-3 1161 356 7809 44 135 40 18 136 19 500
102308-1-4 1107 344 7405 41 121 38 21 134 22 599
102308-1-5 1086 414 7930 57 140 40 21 137 24 456
102308-1-6 1044 389 7464 54 138 40 21 134 20 464
102308-1-7 1375 506 10136 64 153 45 20 139 22 487
102308-1-8 1115 395 7802 54 143 42 19 132 24 494
102308-1-9 1080 398 7566 47 141 39 21 130 23 483
102308-1-10 1168 442 8142 94 136 39 20 141 21 456
102308-1-11 1037 391 7368 51 137 41 19 135 22 500
102308-1-12 1177 442 8365 60 143 40 19 136 22 472
102408-2-1 1428 445 10061 53 149 44 21 142 24 445
102408-2-2 1052 359 7103 45 129 41 19 133 19 447
102408-2-3 932 331 6538 48 124 38 16 129 20 463
102408-2-4 1063 414 7759 50 137 42 17 132 22 466
102408-2-5 1053 359 7631 44 131 40 18 132 22 507
102408-2-6 1016 347 7010 44 128 38 19 133 22 531
102408-2-7 1034 404 7924 49 135 40 18 130 19 472
1A  927 319 8676 nd1 147 42 19 139 24 426
1B  1061 390 8925 nd 149 43 22 141 23 429
1C  744 321 7706 nd 126 36 17 123 20 438
1D  823 320 8000 nd 129 38 19 124 24 439
1E  1076 350 8587 nd 145 39 20 137 25 439
2A  1050 345 8917 nd 149 41 23 136 27 442
2B  1071 366 8829 nd 151 42 18 140 25 435
2C  954 351 8270 nd 137 40 17 134 24 421
2D  1040 341 8715 nd 149 43 21 136 29 433
2E  1038 366 8658 nd 141 42 20 136 29 407

                        1 nd=no data (not measured in earlier study)

Mean and central tendency data for the Vulture raw data above
 

MAJOR OXIDE DATA FOR VULTURE AND ANALYSIS OF RGM-1 USGS SOURCE STANDARD

 

Sample

SiO2

Al2O3

CaO

Fe2O3

K2O

MgO

MnO

Na2O

TiO2

Vulture.

 

 

 

 

 

 

 

 

 

102308-2-1

72.757

14.465

0.874

1.351

6.007

1.45

0.079

2.519

0.239

RGM1-S4

75.680

12.477

1.3024

1.806

4.550

<.001

0.0379

3.77

0.196

 

 

        REFERENCES

Brown, P. (1982) Tracing prehistoric sources of obsidian.  In P.E. Brown and C.L. Stone (eds.), Granite Reef: A Study in Desert Archaeology, pp. 227-241.  Arizona State University Anthropological Research Papers 28, Tempe.

Brown, P.E., and C.L. Stone (1982) Data Base. In P.E. Brown and C.L. Stone (eds.), Granite Reef: A Study in Desert Archaeology, pp. 51-98.  Arizona State University Anthropological Research Papers 28, Tempe.

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. (1995) Sources of archaeological obsidian in the Greater North American Southwest: An Update and Quantitative Analysis.  American Antiquity 60:531-551.

Shackley, M.S. (2005) Obsidian: Geology and Archaeology in the North American Southwest.  University of Arizona Press, Tucson.

Simpson, B.W., and J.R. Mitchell (1989) Gem Trails of Arizona.  Gem Guides Book Co., Baldwin Park, California.

Wilson, E.D., R. Moore, and H.W. Pearce (1957) Geologic Map of Maricopa County, Arizona.  Bureau of Mines, University of Arizona, Tucson.

This page maintained by Steve Shackley (shackley@berkeley.edu).
This research supported, in part, by the National Science Foundation (BCS-0810448)
Copyright 2015 M. Steven Shackley. All rights reserved.
Revised: 27 December 2015

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