TANK MTNS

This is source is the farthest western source in Arizona. The source is located on the Yuma Proving Grounds in the central Tank Mountains UTM Zone 11 809360m Easting by 3673520m Northing, Department of Defense Palomas Mountain Quad 1:50,000 scale, north central Yuma County. The first samples were recovered by John R. Cook during a helicopter archaeological reconnaissance of the proving grounds in 1988. The nodules were within the Quaternary alluvium and embedded within a silicic ash flow. The five nodules analyzed are all less than three centimeters in diameter, but appear to be excellent media for tool production (since this time an additional ten samples have been analyzed some 5 cm in diameter; see Shackley 1991).

The source area was recorded by Rogers as A-111 (SDMOM) as a San Dieguito (Paleoindian) through Amargosa (Archaic) period site (1966:177). Rogers notes that the environment would be sufficient for late period occupation, but he recorded no late material, nor the obsidian nodules. Cook recovered a late period triangular concave based point produced from the Tank Mountain material at White Tanks. A photograph of the tanks in Rogers (1966:70) shows the ash flow tuff environment. The tanks have been eroded into the tuff sediments. Presumably the material has eroded into the local washes, but recent archaeological survey in the area has failed to locate any geological obsidian in surrounding alluvium (Jerome Schaefer: personal communication 1989). The source was published in Kiva (Shackley 1991).

Elemental concentrations for Tank Mountain source standards. All measurements in parts per million (ppm).

SAMPLE	Ti	Mn	Fe	Rb	Sr	Y	Zr	Nb	Ba
WT1	608	389	10256	160	147	28	122	24	946
WT2	564	387	10256	159	145	27	126	19	938
WT3	560	439	10643	167	147	23	124	15	866
WT4	1250	435	10994	172	157	21	118	22	712
WT5	735	418	10302	160	142	22	121	17	870
WT6	647	475	11117	167	149	26	126	22	813
WT7	582	473	11372	178	157	26	129	22	1028
WT8	785	512	11915	181	160	25	129	19	937
WT9	639	442	10687	159	148	24	123	20	946
WT10	563	410	10490	163	149	25	119	20	930
WT12	549	403	10588	161	145	24	124	18	934
LOC 3	661	407	10835	165	147	23	124	18	930
LOC 2-1	668	448	11046	170	151	24	127	20	802
LOC 2-2	618	428	10520	168	149	25	130	21	905
WT11	527	382	10328	152	142	24	120	26	760