Wednesday, April 25, 2018

Mount Holmes, 7,998', Little Rockies, Henry Mountains

Essence: A mountain arises from the surrounding desert. Walk through two rock worlds as the soft red forms of sedimentary sandstone arc up along the flank of the mountain to meet gray, razor-edged igneous intrusives. The concept of a laccolith was developed in the Henry Mountains by G.K. Gilbert in 1877. A brief summary of the geology is included at the end of this post. Located in the Little Rockies sector of the Henry Mountains, this climb is perhaps the most difficult of the high Henry's. Navigation is challenging and so is the rugged terrain. As a point of emphasis, the Henry Mountains are so isolated it was the last range in the West to be placed on a map.
Travel: From the intersection of UT 95 and UT 276, drive 14.8 miles south to where the highway crosses Milk Creek. Pull off the road onto a slim shoulder on the south side of the wash.
Camping: Starr Springs Campground is five miles up a good dirt road. From the junction with UT 95, drive 16.7 miles south on UT 276 and turn right. Water (2018), cottonwood shade, stellar views of the Little Rockies, fire pits, tables, pit toilets, fee, carry out your trash. 
Distance and Elevation Gain: 7.4 miles; 3,200 feet of climbing
Total Time: 5:30 to 7:00
Difficulty: Off-trail; Class 2+ with mild exposure on the summit block; carry all the water you will need. Navigation is challenging. Thank you, John Bregar, for scouting this in 2017 and guiding me up the mountain.
Map: Mount Holmes, UT 7.5' USGS Quad
Date Hiked: April 25, 2018
Quote: Time, geologic time, looks out at us from the rocks as from no other objects in the landscape. Geologic time! How the striking of the great clock, whose hours are millions of years, reverberates out of the abyss of the past! Mountains fall, and the foundations of the earth shift, as it beats out the moments of terrestrial history.
John Burroughs, American Naturalist, 1837-1921

Mount Holmes in evening light from Starr Springs Campground. (THW, photo)

Route: From UT 276, drop into Milk Creek for a short distance and climb back out onto an abandoned road. Walk east between sandstone forms and gain Saddle 5,180'. Scale the north ridge of the mountain, negotiating obstacles along the way. This is an out-and-back.

From the east side of UT 276, elevation 4,940 feet, drop into Milk Creek and hike upstream. The first goal is to locate the old road seen in this image, center-right.

As indicated on the map above, on the descent we returned overland, going in and out of a shallow ravine. Take your pick.

On the ascent, at 0.15 mile we left Milk Creek and climbed south up a blackbrush slope to intersect the old two-track. Follow the road east into Navajo Sandstone domes.

Still on the road, go between a couple of the salmon-colored structures. Below, Saddle 5,180' is image-right.

The road angles up to the saddle at 1.4 miles.

Leave the road just past the saddle and work south (slightly right). Skirt east of a sandstone knoll on a slowly rising traverse. The terrain is globular and complicated. Back up and try another route if you get cliffed out. Clear the knoll at 1.7 miles and gain the north ridge. Cruising up the initial slab couldn't be more pleasant.

A short list of plants includes snakeweed, ephedra, buffaloberry, and piƱon-juniper. It has been a record dry year in the Southwest so not much is blooming. We did see Utah serviceberry and Utah penstemon flowering.

This image gives an overview of the next route segment. Continue up the north ridge and flank the next highpoint, shown behind me, on its left. I spent most of the upclimb aiming for the wrong prominence. It is close to dead center in this image. Of note, there are two tall Douglas fir trees under the north block of the false summit. (THW, photo)

The north ridge is blocked by an igneous sill, shown below. Contour under the gendarme on the east and regain the ridge at 2.6 miles, 6,260 feet.

Upon regaining the north ridge, encounter an outcrop with spiked gendarmes. John Bregar made three alternative passes on a previous trip. He tried going over the top of the ridge, dropping 300 feet into the drainage on the east, and contouring under the obstacle--the best choice. At 2.8 miles begin the sidehill slog.

The transition from sandstone to igneous rock makes the bypass more difficult and somewhat tedious. Watch for teetering boulders and loose material. This is the most challenging segment of the hike. In 0.3 mile, regain the ridge. I found the gravity assist on the return helpful.

The remainder of the climb is intuitive. There is some playful light scrambling. One member of our group hunkered down while we finished the ascent. While sitting silently, a bighorn sheep clattered up the slope. Upon seeing a human, the ram reared up in alarm. Of interest, the Henry Mountains are home to a native herd of bison.

The route works the east side of the ridge before moving west. That's when it became apparent that I was looking at the wrong prominence which is 0.15 mile northwest of the summit, shown. (THW, photo)

The approach over, scale a short blockfield. This image was shot on the descent. (THW, photo)

Climb a steep eastside talus pitch, shown, and then scramble onto the summit. Watch your momentum--it is precipitous up there.

Crest Mt. Holmes at 3.7 miles. The minuscule summit has two relatively flat sitting perches; the peak register is on the west block, shown. Three people can fit on each knob but it is tight. (THW, photo)

The east block opens to an astonishing view of Lake Powell. Visibility was hampered by spring dust but you can make out the La Sal Mountains and Abajo Mountains. (THW, photo)

In this westward panorama, left to right is Navajo Mountain, Mt. Ellsworth, Capitol Reef's Waterpocket Fold, the splintered west ridge of Mt. Holmes (so glad that's not the peak), and Mt. Hillers. (THW, photo)

In the peak register we found a note so compelling I copied it so I could share it with Earthline readers. It was hand written on two sheets of yellow notepaper and carefully stashed in a sealed plastic bag. It reads:

"Today I place this marker here on the summit of Mt. Holmes. This mountain is named after William Henry Holmes. The naming was done by Mr. Hayden of the Hayden Geological Survey. Mr. Holmes was a member of many of Hayden's expeditions and served as an illustrator, cartographer, topographer, and a surveyor. His meticulous drawings and accurate topography are now a part of western lore.

I leave this marker today in memory of another William Henry Holmes of less fame but much accomplishment, also a surveyor. The second Holmes was a mineral and townsite surveyor who staked many mining parcels and laid out the towns of Westcliff and Silver Cliff, CO. To my way of thinking the coincidence of the two Holmes should not go unnoticed so today I place this capsule in honor of two surveyors.

Respectfully set here this 26th day of September, 2009. A fellow surveyor Kit Shy, Westcliff, CO, Shy Surveyors."

Mount Holmes Geology
The geologic discovery of a laccolith occurred in the Henry Mountains. Here's what I learned about laccoliths from John Bregar, geologist. Magma works its way up a vertical conduit into a relatively undisturbed sedimentary section and injects itself between layers that are weakly bonded, initially forming sills, but eventually building up into a giant blister. (A sill is created when magma injects itself parallel to bedding planes and spreads out.) Sedimentary rocks below the blister can remain relatively undisturbed, but sediments above the blister bow up into a dome. Subsequent erosion can remove the sedimentary cover from the dome, exposing the igneous core.

That's the simple textbook description.

Apparent on Mt. Holmes and Mt. Ellsworth (and elsewhere in the Henry Mountains) is a more complex story. Magma intruded in between several weak rock layers, creating multiple sills that can sometimes extend a mile or more away from the main intrusion. We also observe places where the magma between two sedimentary layers suddenly cuts across bedding to higher or lower strata. Adjacent to the main magma blister as it continues to build, these sills, along with the sediments enclosing them, get tilted up, sometimes to almost vertical. Erosion has exposed this complexity on the flanks of the Henry Mountains, and since the sills are generally more resistant to erosion than the adjacent sediments, they often form the tops of mesas, cuestas, hogbacks, and flatirons surrounding the main igneous intrusions. This is readily apparent on the lower part of the Mt. Ellsworth climbing route, where several igneous hogbacks (held up by sills) and intervening soft sedimentary saddles must be negotiated. Sediments involved in this deformation are at least as old as the Chinle or Moenkopi Formations in the Little Rockies.

Of note, nearby Navajo Mountain may look like a volcano but it is also a laccolith. It is exceptional because the sedimentary layers draping the igneous core have not yet been eroded off.

As you ascend into the igneous rock you will notice the gray stone is peppered with white feldspar crystals. These large crystals began to solidify while most of the magma remained liquid, slowly growing in size until the magma was emplaced at a shallow enough depth that the remaining liquid crystallized more quickly, forming the finer-grained ground mass.  Large crystals formed within a fine-grained igneous matrix are called phenocrysts. Igneous rock containing phenocrysts is called porphyry. 

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