The term Wasatch was first used by Hayden (1869:91) as follows:
Immediately west of Fort Bridger commences one of the most remarkable
and extensive groups of Tertiary beds seen in the West. They are
wonderfully variegated, some shade of red predominating. This group,
to which I have given the name of Wasatch group, is composed of
variegated sands and clays. Very little calcareous matter is found in
these beds.
In Echo and Weber Canyons are wonderful displays of conglomerates,
fifteen hundred to two thousand feet in thickness. Although this group
occupies a vast area, and attains a thickness of three to five
thousand feet, yet I have never known any remains of animals to be
found in it. I regard it, however, as of middle Tertiary age.
The Wasatch is well exposed in Fossil Basin. There the unit was regarded
by Veatch (1907) as a group and divided by him into three formations:
the Almy, Fowkes, and Knight. He wrote (1907:88):
In the Wasatch group as thus defined by Hayden the field work of the
season 1905 showed three divisions: 1) a basal member composed of
reddish-yellow sandy clays, in many places containing pronounced
conglomerate beds, which has been named the Almy Formation; 2) a great
thickness of light-colored rhyolitic ash beds containing intercalated
lenses of white limestones with fresh-water shells and leaves—the
Fowkes Formation; and 3) a group of reddish-yellow sandy clays with
irregular sandstone beds (the Knight Formation) closely resembling 1)
lithologically and separated from 1) & 2) by a pronounced period of
folding and erosion.
Veatch, however, erred in his field work and did not realize that the
Fowkes Formation had been downfaulted into the position in which he saw
it (Tracey and Oriel 1959; Eardley 1959). The Fowkes is actually the
youngest of the three formations of Veatch and is considerably later in
age than the true Wasatch.
The Almy and Knight formations are not separable (Oriel and Tracey
1970:16), and can be seen to grade into each other at the basin edges.
[Illustration: Fig. 5. Intertonguing relationship of latest
Cretaceous and Tertiary stratigraphic units of Fossil Basin.]
Recent, Pleistocene
Pleistocene and Recent gravel and alluvium
Pliocene
Gooseberry Member of Fowkes Formation
Oligocene to Pliocene
Hiatus
Eocene
Bridgerian
Fowkes Fm.
Bulldog Hollow Member
Sillem Member
Unconformity
Wasatchian: Wasatch Formation, Tunp Member
Bullpen Member
Green River Formation
Angelo Member
Mudstone Tongue
Fossil Butte Member
Sandstone Tongue
Main Body
Lower Member
Basal Conglomerate Member
Paleocene
Possible hiatus or unconformity
Evanston Formation
Main Body
Hams Fork Conglomerate Member
Latest Cretaceous
Lower Member
UNCONFORMITY
Late Cretaceous
Adaville and older formations
[Illustration: Fig. 6. Subdivisions of Paleocene and Eocene time.]
Eocene
Late Eocene
Uintan
Mid Eocene
Bridgerian
Early Eocene
Wasatchian
Lostcabinian
Lysitean
Graybullian
Paleocene
Late Paleocene
Tiffanian
Mid Paleocene
Torrejonian
Early Paleocene
Dragonian
Puercan
The Almy and Knight, as defined by Veatch, are probably different facies
of Wasatch, the Almy being a more peripheral facies and the Knight a
more basinal facies (Oriel and Tracey 1970). These authors proposed that
the terms Almy and Knight be dropped and that the name Wasatch be
applied to all these rocks to avoid confusion.
The latest subdivision of the Wasatch Formation in the Fossil Basin is
that of Oriel and Tracey. The members of the Wasatch Formation they
propose are described in order from oldest to youngest.