HU Ranch Cataract Gorge

Welcome to HU Ranch! Looking out across the landscape, you will see the cattle ranch in a very linear canyon to the south. The canyon, known as HU Ranch Cataract Gorge (Bretz et al., 1956), or the Davin Coulee (on topographic maps), is an elongated canyon that is cut deep into the land's surface.

This Davin Coulee is a 90-meter-deep gouge that formed when the floodwaters from Glacial Lake Missoula ripped through the area. The main tract of the waterflow was through the Washtucna Coulee to the Northwest. With hundreds of feet of water racing through, some water spilled over the southern edge and fiercely followed the weakened rocks which preferentially ripped out rocks and caused today's distinct coulee. As the fractured rocks were plucked by the glacial floodwaters, the crack grew longer and retreated in the direction of the overflowing waters, which is known as a recessional cataract.

The fragility in the rocks is caused by a generally east-west deformation of the bedrock. As the bedrock slides in a shearing motion along faults, the deformation manifests itself on the surface as weakened and fractured rocks, known as shear joints. We know this deformation started prior to the floods because as the glacial floodwaters violently swept through, the fractured rock was preferentially ripped away in the torrent. Seen in Figure 1, these joints show how flood waters followed them. A similar recessional cataract is seen at Palouse Falls, which runs parallel to the Davin Coulee, the process illustrated in Figure 2.

Images

Figure 1 Map fractures and HU Ranch

Figure 1 Map fractures and HU Ranch

Map of HU Ranch with the ranch area outlined in blue. Dominant fracture sets highlighted with red. The HU Ranch Recessional Cataract or Davins Coulee has zigs and zags at the northern end due to the fractures, but becomes very linear as it approaches the Snake River to the south. | Source: Google Earth Pro | Creator: Alex Fry View File Details Page

Recessional Cataract

Recessional Cataract

Time lapsed images to illustrate the process of cataract formation. | Source: Modified from John Sonnechson's Bretz Flood's | Creator: Cassandra Hennings View File Details Page

Looking south at the HU Ranch Cataract Gorge (Davins Coulee) from the road.

Looking south at the HU Ranch Cataract Gorge (Davins Coulee) from the road.

Creator: Dr. Chad Pritchard View File Details Page

Cite this Page:

Alexander Fry, “HU Ranch Cataract Gorge,” Ice Age Floods Explorer, accessed August 22, 2017, http://floodexplorer.org/items/show/24.

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