City Creek Nature Notes – Salt Lake City

January 6, 2017

January 5th

Filed under: Geology, Pleasant Valley — canopus56 @ 2:52 am

Landslide

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4:00 p.m. Last night another foot of snow has fallen and temperatures have dropped into the teens. Instead of jogging up the canyon, I drive up to the top of Terrace Hills Drive and then jog up to the south-east ridge between the Avenues and City Creek Canyon. The ridge between the Avenues and City Creek is favored by runners because of the dramatic views of the city and, in the distance, of the Great Salt Lake and Antelope Island. It is here that local climbing legend and former Salt Lake City Mayor Ted Wilson would run during the depths of winter’s inversion haze in order to escape the bad air of the city.

I am here to look for a geologic feature in the canyon shown on the Van Horn and Crittenden’s 1987 map and a Salt Lake County geologic hazards map: a large landslide on the west side of the canyon that extends from mile 1.2, picnic site 9, to about mile 2.5. This landslide is not apparent standing on the road between mile 1.0 and mile 2.0, but from vantage point of a peak on the south ridge, I am over taken by immensity of the slide. The leafless trees and winter’s snow emphasizes the shape of the land. Several north-south trending side canyons regularly come off the opposite ridge, but centered near milepost 2.0, it is as if some Titan has deflated the land and its empty billowing shell floats above the bedrock. Pleasant Valley exists because of this landslide – the flatter land of the valley is a run out zone of the slide. Although this feature is undated on these experts maps, the slide must be geologically relatively recent. The stream has not had time to reshape the flat into the archetypal v-shape of a stream cut valley.

The slide has three parts. First, at the down-canyon opening of Pleasant Valley, just up canyon where a natural gas pipeline road climbs up the opposite ridge, there is a large sluff topped by a distinct scallop shape. This slide is not shown on the geologic maps. A few days ago, I watched deer grazing on that hillside (Dec. 31st). Second, beginning at picnic site 12 above milepost 1.5 and continuing to milepost 2.0, there is the large region of “deflated” land shown on geologic maps. Third, a smaller similar slide is near milepost 2.5. None of these landslides are apparent when walking or running up the canyon. The road is set at an elevation closer to the stream and on the north-west of the canyon the slide has created a ledge that hides the view of the much larger slide zone. For several decades, I have jogged on the road underneath these slides several hundred times, and I have been to the south ridgeline on as many occasions, but this is the first time that I have perceived what is now an obvious, large feature of this landscape. The eyes see, but they do not really understand.

As I drive out down Terrace Hills Drive to 11th Avenue and Bonneville Drive, I go past another slide just a few blocks from home. At the corner of 11th Avenue and Terrace Hills is another landslide about one-half mile in diameter, but all evidence of it has been erased. For many years, a gravel pit operated at this corner, but the pit was redeveloped into an elementary school, a park, and a fire station. Surrounding residential homes complete the mask that obscures underlying landslide. The Salt Lake County geologic hazards map show this as an area that may again move in the next major earthquake.

In Thoreau’s “Journal” on January 5th, 1852, he remarks that trees are white-frosted only their storm-side exposed to blowing snow. On January 5th, 1854, he again see small fleas in the snow. On January 5th, 1856, he observes reflected speckles of light from small crystals on the snow’s surface and calls them “crystal stars”. On January 5th, 1859, he compares the constant song of a sole winter chickadee to a man talking to himself. On January 5th, 1860, Thoreau notes that what one sees in nature depends on what a person believes is important in nature or that which has his or her narrow immediate attention. Thus, repeated observation as suggested by Aristotle, are needed to truly know a thing in nature.

On January 5th, 1952, the Salt Lake City Commission approved a plan to increase its drinking water quality as required by the U.S. Public Health Service (Salt Lake Telegram). The plan included closing City Creek Creek above any water intake pipe, building a water filtration plant, moving all toilet facilities at least 50 feet away from the stream, and patrolling the canyon for watershed violations. The water filtration plant was built in 1952 and 1953, and thereafter, the City’s water supply was chlorinated. All public access to City Creek Canyon was closed until 1965. In 1965, the City reopened public access to the water plant at mile 3.4, but the canyon above the plant remained closed. In 1975, public access to the entire canyon was restored (L. Hooten, Jr., History of City Water 1975). On January 5th, 1918, the Treasure Box mine in City Creek Canyon reported striking high-grade ore (Salt Lake Herald). On January 5th, 1883, J. Worthing and S. Potts wagered $80 USD (about $2,056 USD in 2016) that Worthing could catch twice the number of fish from City Creek as Potts (Salt Lake Herald).

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