City Creek Nature Notes – Salt Lake City

January 6, 2017

January 6th

Filed under: milepost 1.5, Picnic site 9 — canopus56 @ 5:22 pm

Lake Bonneville

1:00 p.m. Temperatures remain in the teens today; the Refrigerator (Dec. 28th) continues. While driving to Guardhouse Gate and at the corner of 11th Avenue and Bonneville Drive, I see two another areas of recent landslide activity. On the west side of lower City Creek Canyon along East Capitol Boulevard and north of the Capitol grounds, is another large landslide area shown on the Salt Lake County geologic hazard map. One home owner along East Capitol has constructed three stories of cement block wall below their home as insurance to keep their home from moving. This landslide area continues up canyon to picnic site 3. Turning the corner on to Bonneville Drive towards the canyon, there is a low concrete wall that the City erected to hold back the sliding slope on the east or right side of the road. Jogging up to picnic site 9, then on to milepost 1.5, and turning back down canyon, a rockslide can be seen on the southeast wall at the entrance to Pleasant Valley. This slide is shown on both the Van Horn and Salt Lake County geologic maps, but not being a geologist, I am unsure what the maps refer to. There appears to be a slump at the base of this wall, but there are also large boulders on the hill side that have cleaved from sandstone layers and tumbled downhill.

Jogging downhill, I come to picnic site 7 and then the red bridge at mile 0.9 at an elevation of 4,712 feet. A lay geologic guide to the Wasatch Canyons of the Utah Geologic Survey marks this area where a beach of ancient Lake Bonneville stabilized during 14,000 to 12,500 years ago (Ut. Geo. Survey, n.d.; see Stratford 1999). The Provo Bench of Lake Bonneville frames the lower canyon at Bonneville Drive on the east and below Ensign Peak on the west. The Provo Bench was first identified in G. K. Gilbert’s classic 1890 geologic investigation titled “Lake Bonneville” while Gilbert was employed by John Wesley Powell, the great western river explorer and first director of the United States Geological Survey (Gilbert; Stratford). After the lake first formed about 30,000 years ago, the lake grew and eventually formed the Provo Pleistocene epoch beach that extends up into the canyon near picnic site 7. But this was not the highest level of the lake, and between 16,500 and 15,000 years ago, the lake temporarily reached its highest level at around 5,325 feet, or just below the water treatment plant. While at the lower Provo bench level, City Creek formed a fan-shaped delta below the surface of the water that reached to the present location of the Mormon Temple. Hintze reproduces a fanciful reconstruction by De Courten of Ice Age animals seen from a viewpoint looking south from the vicinity of City Creek and the State Capitol 15,000 years ago (Hintze, 118). At about 11,000 years ago, Lake Bonneville quickly reduced, but paused briefly at 4,250 feet to create the faint Gilbert Shoreline (Hintze, 119, Fig. 152). Then the lake’s level fell to its current level of 4,206 feet, and at that time, the first evidence of human habitation at the fringes of the lake were found in Danger Cave near Wendover, Nevada (id). Because of the rapid reduction in the lake’s level, the resulting high stream velocity was able to crave out of that fan-shaped delta, the v-shaped canyon seen today below Guardhouse Gate and Bonneville Drive. In order to exploit the resource provided by the ancient delta fan, through the 1910s, a gravel pit operated in the lower canyon in the location of Memory G6rove (Salt Lake Tribune, April 12th, 1911).

Driving downtown after my jog, I turn back and look at the hillside above Warm Springs on Beck Street. There is a fainter lower terrace at about 4,500 feet elevation that Gilbert named the Stansbury Bench (Stratford, 369; Hintze, 119). Some years ago when I worked downtown during lunch, I would run up to the Stansbury bench west of the State Capitol building. This lower bench was created between 30,000 and 16,500 years ago as Lake Bonneville was first forming (Stratford, 369). Looking to the west and Antelope Island, the three benches, the Bonneville, Provo and Stansbury benches, can be seen carved on its eastern side; however, the bench elevations on the Antelope Island are higher than the elevations of the corresponding benches on the western side of the Wasatch Mountain Front Range in and near City Creek. Gilbert first noted this in 1890, and he reasoned that the weight of 1,000 feet of water had pushed the land down as the beaches were forming (Stratford 369-370). After the waters receded, the land at the center of the lake rebounded and raised the benches.

In Thoreau’s “Journal” on January 6th, 1838, he describes a mixture of star-shaped snowflakes and round grapple snow.

On January 6th, 1939, the Utah Audubon Society planned a monthly field trip up City Creek Canyon (Salt Lake Telegram). On January 6th, 1883, two miners attempted to reach Snell’s mine more than seven miles up City Creek Canyon. After traveling two miles in neck deep snow, one miner collapsed from exhaustion, the second miner made it back to the City exhausted, and the first miner was rescued the following day with frost-bitten, black feet.

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