Cedar Mountain Formation
Cedar Mountain Formation
Type
Geological formation
Age
Late Cretaceous
Lithology
Location
Region
North America
The Cedar Mountain Formation
is the
name given to distinctive sedimentary rocks
in eastern Utah that occur between the un-
derlying Morrison Formation and overlying
Naturita Formation (sometimes incorrectly
called the Dakota Formation). It is composed
of non-marine sediments, that is, sediments
deposited in rivers, lakes and on flood plains.
Based on various fossils and radiometric
dates, the Cedar Mountain Formation was
deposited during the last half of the Early
Cretaceous, about 127 - 98 million years ago
(mya).
The drab-colored lower portion of the Cedar
Mountain Formation overlying the brighter
Morrison Formation.
Dinosaurs occur throughout the forma-
tion, but their study has only occurred since
the early 1990s. The dinosaurs in the lower
part of the formation differ from those in the
upper part. These two dinosaur assemblages,
characterized by distinct dinosaurs, show the
replacement of older, European-like dino-
saurs with younger, Asian-like dinosaurs as
the North American Continental Plate drifted
westward. A middle dinosaur assemblage
may be present, but the fossil record is not
clear.
The formation was named for Cedar
Mountain in northern Emery County, Utah,
where William Stokes first studied the expos-
ures in 1944.[1] Only recently did the 125 m
(410 ft) thick formation get subdivided into
smaller, distinctive beds called members.
There is a debate as to whether there are five
members[2] or four[3] depending whether the
Buckhorn Conglomerate is considered to be
at the top of the Morrison Formation or at
the base of the Cedar Mountain Formation;
most geologists and paleontologist consider it
part of the Cedar Mountain Formation. In as-
cending order the remaining members are
the Yellow Cat Member, Poison Strip Sand-
stone, Ruby Ranch Member, and the Mussen-
tuchit Member. Each of these members are
named after a geographic area where they
were first studied.
Stratigra