70 KECONNAISSANCE OF PAKT OF WESTERN ARIZONA. 
Thick- 
Yellow clay 
Blue waxy clay 
Yellow clay 
Blue waxy clay 
Blue shale (sand mixed) 
Blue waxy clay 
Blue shale 
Blue shale (sand mixed), yielded hot water 
Red shale 
Blue shale • 
Red shale 
Blue shale 
Red "keel" stone 
Water, sand, gravel, and bowlders 
Sedimentary sandstone (brown) 
Red sandstone 
Red shale (burned) . 
Trap rock (dark brown) 
Red shale (burned) 
Lava rock with calcite crystals 
Red sandstone 
Red clay (sticky) 
Volcanic deposit, ash, and bowlders 
(Gas under pressure sufficient to raise 6,200 pounds of tools 400 feet.) 
Bowlders (cemented) 
Cavity 
Bowlders 
Cavity 
Granite with cavities and gas 
1,998 
At the risk of carrying comparisons too far, attention is called to 
the possible correspondence between the Quaternary epochs of 
western Arizona and those of the Lake Bonneville basin. The high 
stages of Lake Bonneville have been explained as being due to the 
changes of climate toward increasing precipitation, and the low- 
water stages toward increasing aridity. Periods of great precipitation 
(and high water in an undrained lake) are those of active stream 
erosion, and, other things being equal, the periods of sedimentation 
in Lake Bonneville should be the periods of stream erosion in neigh- 
boring regions. On this assumption Gilbert's first Bonneville epoch 
of high water, during which 2,000 feet or more of sediment consisting 
largely of fine material was deposited, seems to correspond in dura- 
tion and position in the time scale to the erosion of Grand Canyon 
(epoch 6 of the Arizona scale); his first epoch of low water, to the 
deposition of the Temple Bar conglomerate; his second Bonneville 
epoch of high water, to the erosion of Black and Boulder canyons 
(epoch 8 of Arizona); and his final epoch of desiccation, which was 
ness 
(feet) . 
Depth 
(feet). 
34 
722 
117 
839 
9 
848 
210 
1,058 
18 
1,076 
13 
1,089 
45 
1,134 
71 
1,205 
12 
1,217 
70 
1,287 
24 
1,311 
28 
1,339 
6 
1,345 
70 
1,415 
35 
1,450 
95 
1,545 
35 
1,580 
36 
1,616 
56 
1,672 
14 
1,686 
68 
1,754 
48 
1,802 
105 
1,907 
6 
1,913 
9 
1,922 
22 
1,944 
6 
1,950 
48 
1,998 
