City Creek Nature Notes – Salt Lake City

July 14, 2017

July 14th

An Upside Down Side Canyon

2:00 p.m. Today, I drive 4.3 miles up-canyon to Freeze Creek, an north trending side canyon that begins at Lower Rotary Park. The side canyon leads uphill to Mueller Park below Unnamed peak at 8283 feet. The trail was probably constructed in the 1920s by the Rotary Club, and the canyon supports piping and a cement encased natural spring that delivers water to the picnic area below. What I like about the Freeze Creek hike is that the canyon is, botanically, upside down. Because the canyon rises towards the north, it spends most of its time in perpetual shade, and thus, the canyon is colder at the bottom than at the top. The hike begins at its lowest elevation along a stream and through a grove of Lodgepole pine, a tree that normally grows at colder and higher elevations, and then ascends through tall maple trees and Quaking aspen trees. Off in the distance of this lower part of the Freeze Creek, I can hear the taping of a Downy woodpecker(Picoides pubescens). Then as the trail exits higher into warming sunlight, open grassland appears that ends at an impenetrable forest of Gambel’s oaks. To the east of the oak forest, a Birchleaf mountain mahogany grove can be penetrated, and after a few minutes of effort, access to a trail that leads to Mueller Park Grove is gained.

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On July 14th, 1906, the Salt Lake Herald published two panoramic photographs of Salt Lake City by George Mortimer Gutch. One contrasted downtown Salt Lake City at 200 South Main and the second was taken near the top of Smuggler’s Gulch on Black Mountain, City Creek Canyon. On July 14th, 1886, City Engineer George Ottinger and work crews were cleaning out the City Creek stream bed of debris in order to increase water quality (Salt Lake Herald).

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September 20, 2016

September 1st

Fault

7 p.m. After the canyon opens up at mile 1.3, the first expansive view of the upper canyon occurs at milepost 1.5. On the north side of the upper canyon is unnamed peak at 8283 feet in altitude and on the south side is Black Mountain. Just up canyon of unnamed peak 8283, two fins run down the peak’s flank. In the sunset light, the closest is tan in the farthest is grey. The two fins descend down to a Depression era picnic area, upper Rotary Park, then climb Black Mountain. The grey fin is the main geologic attraction of the Upper Rotary Park picnic area at mile 5.75. There, the fin creates a vertical gully at the end of the paved road where it becomes a horizontal inclined ledge runs along the top of Black Mountain. Runners, who participate in the annual June Wasatch Steeplechase, and more energetic hikers will be familiar with this ledge. It is a jumbled rock scramble that takes considerable time to traverse. A 1987 geologic map by Van Horn and Crittenden (U.S.G.S. I-1762) reveals the scene’s geology.

On the canyon’s north side and at the western base of unnamed peak 8283, Freeze Creek , a north-south running side canyon, begins at Lower Rotary Park at mile 3.75. Freeze Creek marks a major geologic division in the upper canyon. Freeze Creek contains a normal fault. To the down canyon west side of the creek are layers of young Tertiary rock. On the up canyon east side of the creek and running up to unnamed peak 8283, the rocks consist of the some of the oldest layers of stone in the Wasatch. From there and continuing to the 9100 foot Grandview Peak, hidden behind the unnamed Peak 8283, the surface is 500 million year old Cambrian rock. At one point along the Freeze Creek trail up to Rudy’s Flat, recent lake bed sediment sits next to 500 million year older Cambrian rock. The transition occurs because a normal fault along Freeze Creek has raised the up-canyon side faster than the down-canyon side. Erosion has erased the intervening time between them. (Van Horn and Crittenden call the normal fault the Rudy’s Flat Fault.)

On the north side of the upper canyon and descending the flank of unnamed peak 8283, rocks layers are in reverse chronological order: Cambrian, Devoian and Mississippian. Titanic geologic forces have turned the stones upside down from their original deposition. The older Cambrian rocks are higher on the mountain and proceed to younger strata are at the Lower and Upper Rotary picnic areas.

On the south side of the upper canyon, the canyon wall rises to Black Mountain and the geology is even more contorted. Although hidden by a ridge from my viewpoint at mile 1.5, a thrust fault rises south south east from lower Rotary Park to Smuggler’s Gap at the eastern end of Black Mountain. There the thrust fault makes an abrupt 135 degree turn and runs horizontally southwest along the top of Black Mountain. The thrust fault creates the rock scramble ledge along the top of Black Mountain. Here again the thrust fault reverses the order in which rock layers were originally deposited. On the higher canyon side of Black Mountain’s summit is older Mississippian rock while on the cityside, visible from the Avenues neighborhood, the rock is of the younger Permian age.

Faults are also responsible for two miniature rapids in the canyon. The Freeze Creek fault creates on at the overlook in Lower Rotary Park at mile 4.5. A second fault creates another mini-rapid at the Weeping Rock Memorial Grotto campsite at the bridge into the last campsite at Upper Rotary Park near mile 5.5.

A 2009 Salt Lake County geologic hazards report shows that none of these faults have been recently active. However, the thrust faults have also shattered the rock in adjacent Red Butte and Dry Fork Canyons. The University of Utah Seismology Department has recorded about 23 small earthquakes at less than 2.0 magnitude and one earthquake between 2.0 and 4.0 magnitude at a small complex of faults in Red Butte between 1967 and 2003. They recorded two earthquakes between magnitude 2.0 and 4.0 in Dry Fork Canyon at the base of Black Mountain.

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