Autumn on Laramidia’s Ancient Shore

November 26, 2020

Autumn on Laramidia’s Ancient Shore

Photographer: Ray Boren 
Summary Author: Ray Boren

During the Late Cretaceous Periodbefore the rise of North America’s Rocky Mountains, and before the Colorado Plateau emerged to geologically dominate the Four Corners region of Arizona, Utah, Colorado and New Mexico — a vast Western Interior Seaway covered much of the continent’s center, dividing it into two landmasses. The big islands have come to be called Appalachia (to the east) and Laramidia (on the west).

A cliffy portion of the lithified western shore of that inland sea stretches across the background of the autumn-splashed photograph seen above taken along State Road 14, a scenic byway in upper Cedar Canyon above Cedar City, Utah. The shimmering leaves of Utah’s state tree, the quaking aspen (Populus tremuloides), are revealing their inherent yellow pigments. Due to autumn’s chillier temperatures and declining daylight hours, they have ceased producing chlorophyll, which tints the leaves green in spring and summer.

Sediments eroding from now-vanished mountain ranges to the west — on Laramidia which stretched from what is today Mexico to Alaska, and which gets its name from Laramie, Wyoming — were deposited in rivers, lakes and swamps along the seaway 66-100 million years ago. These transformed over time into Cedar Canyon’s tan-to-brown, cliff-forming sedimentary Straight Cliffs (Tibbet Canyon Member) and Wahweap formations. These are also the oldest rocks in Cedar Breaks National Monument, just up the road, along what is today the edge of the Colorado Plateau’s western Markagunt Plateau. Photo taken October 15, 2020.

Photo Details: Camera NIKON D3200; Exposure Time 0.0020s (1/500); Aperture ƒ/11.0; ISO equivalent 400; Focal Length (35mm) 30