278 
along the axis of the Bridger Basin, 
which is a broad, shallow rock-trough 
or syncline between the Wind River 
Range of Wyoming and the Uinta 
Mountains of Utah. Eocene sedi- 
mentary rocks dip gently from all 
sides toward this northeast-southwest 
trending axis. Along the central por- 
tion of the basin the uppermost rock 
exposures are the drab, greenish, or 
varicolored strata of the Bridger 
formation. Beneath these rocks are 
the gray to dark shales that weather 
white, and the grayish-yellow sand- 
stones of the Green River formation. 
These strata, in turn, overlie the red- 
dish and greenish Wasatch formation, 
whose outcrops, except for a few small 
gaps, completely encircle the Bridger 
Basin with a striking zone of color. 
The Green River, which drains the 
basin, originates in large part on the 
west slope of the Wind River Range 
and flows southwestward through 
colorful badlands in the Wasatch 
formation to Labarge, Wyo. There 
it turns southeastward and in a 65-mile 
course through Green River and Brid- 
ger strata bisects the basin before 
veering south near Green River toward 
the Uinta Mountains. 
The landscape of the Bridger Basin, 
carved out by the Green River and its 
tributaries, is at a general elevation 
of 7,000 feet and comprises open grass 
and sagebrush plains, broad, cotton- 
wood-lined valleys enclosed by low 
hills, and occasional mesas or buttes 
with precipitous slopes or desolate, 
dissected badland borders. 
When found undamaged and stand- 
ing upright in the sands and shales of 
the Green River and Bridger forma- 
tions, the pillars are usually well 
rounded at the top and sides, are with- 
out an orifice of any kind, and are 
gray to brownish in color. Casually 
observed they look like columnar con- 
cretions or stumps of fossil wood whose 
tops were rounded by weathering. 
They may extend into the ground for 
several feet and their more or less 
irregular, sometimes spreading, flat 
bottoms rest on shale without any 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1948 
evidence underneath of a vent, such 
as should be expected were they true 
geyser cones. Moreover, the ground 
and bedrock in their immediate vicin- 
ity show no evidence of hot-spring 
action, such as tufaceous or sintery 
sheet and terrace deposits. The land- 
scape of the Bridger Basin is developed 
in fresh-water strata, which, at the 
sites I visited, are not faulted, and 
the nearest outcrops of igneous rock 
or surface evidence of volcanic activity 
are 30 miles distant. ‘Therefore, a 
visible, possible cause or source of hot 
waters, and fractured rocks permitting 
their emergence from subterranean 
depths, is not present in the Whisky 
Basin area. 
Let us examine these pillars more 
closely. Their outer surface is rel- 
atively smooth but may be warty or 
tuberculated and may be broken as a 
result of spalling, the curved, shelly 
fragments strewing the ground in the 
vicinity. Roughly transverse frac- 
tures or joints are sometimes present, 
causing the specimens to disintegrate 
into thick, millstonelike sections (pl. 
2, fig. 1). Inside, a typical cross sec- 
tion (pl. 3, fig. 1; pl. 5, fig.)2)eshows 
well-marked inner and outer zones 
distinguished by color, minerals, and 
the ‘“‘growth” lines indicating the 
direction in which the zones “‘grew” 
by the addition of successive layers of 
mineral matter. 
The inner zone may consist of an 
irregular opening lined with translu- 
cent or banded chalcedony (agate) 
(pl. 5, fig. 2), sometimes with quartz 
crystals projecting inward (pl. 3, fig. 1), 
thus simulating a geode. ‘The center, 
however, may be completely filled with 
chalcedony and quartz, or it may, in 
addition, have crystals of calcite, or 
may be composed entirely of calcite. 
Relatively rarely it may contain a 
piece of fossil wood (pl. 7). Clearly, 
the beginning of chalcedony banding 
was at the outermost boundary of 
chalcedony (pl. 3, fig. 1; pl. 5, fig. 2) 
and proceeded inwardly in successive, 
parallel layers or bands until quartz 
or calcite crystals ended this phase of 
