Deschutes Formation, Whychus Creek Geologic Field Trip

Deschutes Formation, Whychus Creek Geologic Field Trip

May 10, 9 am-4 pm, led by Derek Loeb

 The Deschutes Formation ranges in age from approximately 7.5 to 4 million years old and consists of volcanic deposits and associated sediments that were predominately sourced from the east flank of ancestral High Cascades. While the Deschutes Formation is present over a large portion of the upper and middle Deschutes Basin in the greater Bend area, to the south it is buried under younger volcanic deposits sourced from the Cascades Range to the west and Newberry Volcano to the south. North of Bend the Deschutes Formation comprises much of the surface geology and is especially well exposed in the canyons of the Deschutes and Crooked Rivers and Whychus Creek. The Deschutes Formation is of particular interest because, not only is it the best way to understand the evolution of the ancestral, High Cascades, but it serves as the major groundwater aquifer in the area.

This field trip will visit two sections of Whychus Creek that are representative of the range of lithologies that make up the Deschutes Formation and its transition from being dominated by volcanic rocks to the west and transitioning to a much greater sedimentary composition to the east. The first stop will be at Whychus Canyon Preserve, owned by the Deschutes Land Trust, where we will do a fairly level, 1-mile hike to an outcrop and viewpoint that is representative of the volcanic facies of the Deschutes Formation. We will then drive to the Alder Springs trail head, on the Crooked River National Grasslands, and do a 3-mile hike with an elevation change of 400 feet to the banks of Whychus Creek. Along the way we will see numerous outcrops showing the transition to the sedimentary facies of the Deschutes Formation and its importance as an aquifer.

This field trip is scheduled for Thursday May 10, from 9 am to 4 pm. The hiking is rated as moderately challenging. The hike into and out of the canyon at Alder Springs has some relatively short but steep sections and it can be hot this time of the year. This field trip is suitable for all levels of background in geology. This will be a good introduction to those who are not familiar with the Deschutes Formation or these outcrops, and for those who are, this is a good chance to become reacquainted and engage in some lively geo-discussions. This trip is led by Derek Loeb and is limited to 12 participants.