Saddle Mountains Intercanyon Flow
The geological story of the Devil’s Canyon and its creation is complex but the layers may be peeled away for a fuller understanding.
Saddle Mountains Intercayon Flow Complex
The geological story is not explained by looking at the dry canyon floor but looking east of the road to the flood basalt layered hill. This is where the story is told. During the waning and last basalt floods of the Columbia River Basalt Group was the Saddle Mountians flows 5.5 -14 Ma (million years ago). Saddle Mountains basalt flood was made up of many individual member flows. Three of those flows are seen here. The oldest is the Esquatzel member some 12.5 Ma. The later flow of the Pomana member 12 Ma. and the youngest Elephant Mountain member 10.5 Ma. A mystery emerges to why the Pomana and the Esquatzel members are next to each other rather than over flowing one another.
Geological Story Board of the creation of Devil’s Canyon
Follow the figures below from ancient to present to answer the mystery.
Please Note: Figures are for explanation purposes only and are not to scale.
Fig 1. 16.7 Ma the Grande Ronde began to lay down basalt over the ancient Columbia Basin. 15.6 Ma Frenchman Spring member of the Wanapum Basalt flood was laid over the Grande Ronde Basalt.
Fig 2. Between 15.6 Ma but before the Snake River was pushed north because of the uplift of the Blue Mountains (apx 15-5 Ma), the ancient Salmon River flowed from Idaho through the Columbia Basin on its way to the Columbia River gouging out the Devil’s canyon. The canyon was part of the natural flow of the river.
Fig 3. 12.5 Ma the Equatzel member lava flowed from a fissure about 40 miles to the east. It flowed down the Salmon River. The lava flowed during a dry season for the Salmon because of the lacking evidence of basalt pillows, embedded turf or clasts.
Fig 4. The Salmon River kept its course even after the Equatzel basalt filled part of the river’s bed. The river continued and carved part of the canyon floor out again.
Fig 5. 12 Ma the Pomana member lava flowed from fissures about 150 miles to the east in Idaho. The Pomana flow once again took the path of least resistance and flowed down the Salmon River. The basalt filled the lower portion of Devil’s Canyon to the level of the Equatzel flow. The Salmon River kept its course even after the Pomana basalt filled the river bed. The river continued to flow down the canyon.
Fig 6. 10.5 Ma the Elephant Mountain member lava flowed from fissures 70 miles to the southeast. Elephant Mountain member took the same path down the Salmon River and over flowed both the Pomona and Equatzel members. This time the flow filled the canyon and diverted the Salmon River to the current Snake River location in this area.
Fig 7. 13,000 and 15,000 years ago, the Lake Missoula flood waters poured through an ice dam near Clark Fork, Idaho and ran across the Columbia Basin. The water flowed down the Washtucna coulee and then down through Devil’s canyon carving out the old basalt leaving the Saddle Mountains Intercayon Complex as seen from final.
To log this Earthcache; Please send a private message to me with answers to the following questions.
1. What finally diverted the Salmon River from flowing down the Devil’s Canyon?
2. Compare and contrast the texture of the three members as seen on the escarpment?
3. Does the Equatzel member continue across the canyon? If so, how do you know?
Optional:
You may upload a photo to the page of any local wildlife, unique vegetation or geology in the area.
Additional study and sources:
Video: Esquatzel Basalt
Video: Ancient Rivers of the Pacific Northwest
Stratigraphy and tectonics of the central and eastern portions of the Columbia River Flood-Basalt Province: An overview of our current state of knowledge, Pgs 667-669
Palouse Falls to Lower Monumental Dam, Stop 6
Goldschmidt Conference 2005: Field Trip Guide to the Columbia River Basalt Group