City Creek Nature Notes – Salt Lake City

September 21, 2016

September 8th

The Mountain Who Lost It’s Backside

4 p.m. Today I decide to drive up to the end of the paved road and trail jog to the end of the canyon. The canyon will be closed to cars at the end of September, and I usually do one of these trail runs at this time. (A second is done in early June.) The paved road ends at mile 5.75 and the trail continues for another 4.25 miles before it descends into Wasatch County. But today I decided to only go to trail mile 3.5 where one can see that part of the backside of Grandview Peak is missing. It is the sheer vertical cliff about 200 feet high.

Through trail mile 1.0, the stream is wider and flat. The trail is about 100 feet off to one side and passes through box elder and maple groves. The trail, actually a dirt road that is fading away, crosses the stream at two iron bridges and passes the Smuggler’s Gap trailhead. Then the trail changes character. The trail becomes a disused single track that sits two or three feet to the north of the small fast-moving creek. The creek flows over a series of algae covered rock jumbles into small pools. Both the stream and the floor of the trail are broken Mississippian and Permian slate. At times the stream and trail wind through boughs of river beech trees. Here, a red Admiral butterfly floats between the stream, bushes and the shade of the trees.

Grandview Peak is to the left and the north, but its view is blocked by the steep v shape of the creek gorge and by stands of aspen. To the right and south is the ridge between City Creek and Red Butte canyons. On the city side the ridge is a near-vertical wall that sits in perpetual shadow. Thus, it is covered in the thick healthy stand of cold tolerant Douglas fir. In contrast, the Sun exposed Red Butte side is a thick drought tolerant Gambel oak forest.

I round a bend near trail mile 1.6 and startle a Cooper’s hawk that is napping in a tree grove. Attempts to fly away but is trapped in the tangle of branches that it is resting in. It waits anxiously for about 30 seconds. Seeing that I am no threat, it picks a route out of its lair, and then like an owl, expertly flies through the forest understory to freedom.

At trail mile 2.1 the canyon opens into the first of four hanging meadows. Each is divided by gradual inclines. This first meadow hosts a SNOTEL weather station, and in the second at trail mile 2.6, the bushes are flattened in a series of circles. Here a moose can usually be found, and today is no exception. As I am exiting the meadow, I hear something crashing through the brush, and turning around, a frightened female moose is careening into the safety of the forest. There is little sign of deer in this part of the canyon because there is little grass forage to support them. In each of these hanging meadows there are bushes of mountain blueberries that provide refreshing forage for me.

The character of these meadows has changed dramatically since I last ran through them in June. Then the brush was so profuse that it reached my neck and overhung and obscured the trail. Jogging was an act of faith and was more like swimming through a sea of green. You hoped that the trail was underfoot and sometimes it was not. Now the meadows are a sea of tan. The trail is plainly visible, but the trail floor is a pallet of dark browns and tans from dried and crushed brush punctuated by accents of fallen bright and muted red-orange aspen and maple leaves. I am jogging over an 18 inch by 300 foot canvas painted by the randomness of nature.

At trail mile 3.6, I am climbing past the last meadow and towards the ridgeline at the end of the canyon. My goal for the day is visible on the north side of canyon. Here a series of spur ridges come down from Grandview Peak and end in rounded noses, but one nose is cut off. It ends in a sheer vertical cliff about the size of two or three football fields. At its base is a 200 foot tall talus field. Here, some geologists believe an ancient earthquake may have shorn the mountainside away. One can see other examples along the Wasatch Front. The shear north face of Mount Olympus has a rubble pile at its base which is now the Mount Olympus subdivision. This reminds us that the West is earthquake country and there work 14 earthquakes in Utah of greater than magnitude 5 during the last century. In 2008, geologists Francis X. Ashland and Gregory N. McDonald investigated the Grandview Peak landslide in order to determine the most cost-effective method of dating the mountainside’s failure. They concluded that the remoteness of the site and the depth of the talus field made it impractical to retrieve rock samples from deep underneath the talus field in order to accurately date when the slide occurred.

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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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