NO. 4 GEOLOGY, WIND RIVER BASIN—TOURTELOT 13 
formation is made up of gray and greenish-gray andesitic volcanic 
sedimentary rocks and the upper part is tan volcanic siltstone. The 
greenish-gray unit has a maximum thickness of about 200 feet and 
the siltstone unit has a maximum thickness of about 350 feet. Single 
exposures of the lower unit do not reveal more than about 150 feet 
of strata. The siltstone unit is the youngest part of the sequence and 
its top is an erosional surface; the original thickness of the siltstone 
cannot be determined. 
The Hendry Ranch member is consistent in its major lithologic 
characteristics and is easily recognizable wherever seen, even in areas 
of only partial exposure. The member is confined to isolated areas 
of outcrop, and no facies changes were detected. 
The greenish-gray volcanic claystone and siltstone weathers to 
smooth badland slopes at most places. In general, the rocks in the 
greenish-gray unit are finer grained than the rocks in the underlying 
green and brown member. Irregular ledges of harder and more limy 
siltstone and sandstone are present in some exposures and one such 
ledge is particularly prominent at localities 6 and 7 (pl. 1). Thin 
beds of gray to black waxy claystone are present in the upper part 
of the same exposures. Crystals of selenite are abundant on the sur- 
face of most outcrops. Local lenses of fine-grained chert and quartz 
pebble conglomerate are interbedded with the tufts. 
The volcanic material in the rocks corresponds in composition to 
an andesite. The plagioclase feldspar is andesine, instead of labra- 
dorite as in the green and brown member of the Tepee Trail forma- 
tion. Not enough petrographic work has been done on the Tepee 
Trail to evaluate the significance of the apparent difference in feld- 
spars in the two members. Light-tan to greenish-brown biotite and 
hornblende are abundant and a few delicate shards of altered glass 
are present in most thin sections. 
At many places the rocks weather to a nodular surface very simi- 
lar to the “nodular zones” of the Oligocene sequences in Nebraska 
and South Dakota. Some of such nodular zones have been inter- 
preted as parts of paleosol complexes by Schultz, Tanner, and Harvey 
(1955). The nodular zones in the lower part of the Hendry Ranch 
member contain Glypterpes, cf. G. veternus, a large land snail, and 
also clay- and calcite-filled borings similar to the fossil larval cham- 
bers of insects described by Brown (1934, 1935), apparently indicat- 
ing subaerial conditions during deposition of the rocks. The nodules 
have yielded most of the fragmentary fossil vertebrates found in the 
Hendry Ranch member, a type of occurrence typical of the paleosol 
complexes reported by Schultz, Tanner, and Harvey (1955). 
