D1 Synorogenic Strata:
This layer is composed of approximately 1,500 feet of alternating layers of sandstone from ancient river channels and mudstone from ancient flood plains. These layers were deposited during the early part of the uplift of the Front Range by rivers similar to the modern Platte River in northeastern Colorado. D1 Synorogenic Strata are coarse-grained along the Front Range and become fine-grained and coal-like to the east. These sediments were deposited in the Cretaceous Period and Paleocene Epoch (68-56 m.y.a). Typical fossils include petrified wood, leaves, dinosaur bones, and mammal teeth.

Denver Formation (Paleocene):
A sedimentary unit rich in volcanic debris typified by exposures on South Table Mountain west of Denver. Our terminology ascribes the Denver Formation to D1 Synorogenic Strata. Typical fossils include palm and sycamore leaves and mammal teeth. The Castle Rock Rainforest site is located at the top of this unit, and the Denver International Airport fossil site is near its base.

Click On Layers
A) Fossil leaf
B) Denver Formation exposed in the Denver International Airport (DIA) construction site.
C) Reconstruction of DIA as it appeared 65 million years ago.
D) Outcrop of coal seam with layers of volcanic ash.
E) Fossil mammal skull.


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