The Dawson Arkose consists of
alluvial fan and
fluvial deposits that accumulated at the foot of the growing
Rocky Mountain Front ranges. It overlies and interfingers with the
Denver Formation which spans the
Cretaceous-Paleogene boundary, and is of early
Paleocene (
Puercan) age. In 2002 the Dawson Arkose was included as part of a larger unconformity-bounded unit named the D1 Sequence, in order to facilitate basin-wide studies and avoid confusion arising from the lateral and vertical
facies changes that occur within the Denver Basin. The base of the D1 is marked by the abrupt facies change at the top of the
Laramie Formation, and its top is placed at the base of a regional
paleosol series. The
Arapahoe Formation and the Denver Formation are also included in the D1 Sequence. ==References==