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Hike to the top of a collapsed stratovolcano in Arizona's alpine tundra for a view of the Grand Canyon (on a clear day).
On top of Arizona: a spectacular look toward the east at the Inner Basin sculpted by San Francisco Mountain avalanche that occurred as a result of caldera collapse, and the San Francisco Volcanic Field in the distance.
Sue and Fred on top of Humphreys Peak among rocks that are the remains of a huge stratovolcano caused by Great Basin stretching that brought mantle rock higher to the surface.
Trip Stats via Snowbowl Trailhead
Location: Coconino National Forest - Kachina Peaks Wilderness - San Francisco Mountains, Flagstaff, northern Arizona. Distance/Elevation gain: 4.8 miles from parking lot (9,266') to Humphreys summit (12,633') = 3,367' gain (9.6 miles out and back). Trailhead: From Flagstaff drive north on US 180 for 7 miles to FR 516, the Snowbowl Road. Drive 7.4 miles on this paved road to the lower parking lot of the Snowbowl facility. The trailhead is located at the north end of the parking lot. Forest Service info: Humphreys Trail #151) Factors that make this hike more difficult: high altitude. Date Hiked: October 7, 2024. Prominence: 6,039'. Maps/Apps: Humphreys Peak Quad topo map, AllTrails. Interactive Caltopo map of the San Francisco Peaks and Flagstaff Area. with our GPS tracks. Considerations and links: Mountain Weather Forecast - Humphreys Peak. Flagstaff Rangers District. Geology: Humphreys is the highest of the San Francisco Peaks (Agassiz and Aubineau are two others), of a much taller San Francisco Mountain, which was a large stratovolcano composed of layers of lava, cinders, pumice and ash that erupted over 900,000 - 400,000 years ago. After this, the top and northeast side of this stratovolcano collapsed in a gigantic avalanche that flowed out toward the northeast. Stratovolcanoes are steep because the extruding lava is high in silica (geology term is felsic - quartz and feldspar forming) and therefore has higher viscosity, so it solidifies more quickly, creating a steep profile.
Related Posts in Arizona
The remnants of a much higher stratovolcano, Humphreys Peak stands higher than any other summit in Arizona, with an additional advantage of having the second-highest prominence. Prominence is a measure of the difference in elevation between the summit and the lowest point along the ridge that connects the mountain to a higher mountain (from surgent.net). Both Fred and I hiked this this summit 30 years ago, separately. The aspect I remember most, aside from the false summit, was the view of the Grand Canyon to the north. This time it was a bit too hazy to see the Grand Canyon, but I could see the Painted Desert in the distance. As with other summits, Humphreys has a couple of "false summits". In fact, on our way down, a guy hiking up was grumbling about the false summit he was on and that the trail was a bit hard to follow occasionally. But we knew what to expect this time: the first summit you see is not Humphreys; it's hiding behind it. The altitude is the most limiting factor of this hike, especially if you are coming from a lower elevation.
Our Hike
Trailhead to forest switchbacks (0 - 1.0 mile, 9,266' - 9,940') Forest switchbacks to saddle on Humphreys' south ridge (1.0 - 3.8 miles, 11,780') Ridge to Point 12, 297 (3.8 - 4.2 miles, 12,297') Point 12,297' to summit (4.2 - 4.8 miles, 12,633')
The Arizona Gondola of the Arizona Snowbowl Ski Resort is visible across the valley to the south as the trail progresses up to Humphreys' south ridge and a spectacular view to the east. Here, and the rest of the way to the summit, you see different views of the massive avalanche topography that occurred hundreds of thousands of years ago when the eastern flank of San Fransisco Mountain collapsed, leaving six peaks lining the ridge above it.
Agassiz Peak is one of them, a large peak to the right (south), and from what I read of other trip posts, illegal to climb unless there's snow to cover a federally-listed threatened plant, the San Francisco Peaks groundsel. It grows only in the alpine tundra of the San Francisco Peaks at 11,000 - 12,400' elevation. It thrives in the volcanic rock talus on Humphreys and Agassiz Peaks. We did see one sign - "Hiking off trail prohibited - $500 fine" at the ridge. At the saddle on the ridge, the Weatherford Trail heads southeast towards Agassiz, Fremont and Doyle Peaks that line this huge avalanche chute, which is referred to as the "Inner Basin." It looks so tempting to go back and summit these mountains, but for Agassiz it would have to be with snow cover. Now it's just a matter of hiking through a steep volcanic talus slope, arriving at a "false summit" before you actually get to Humphreys, another 0.5 miles, straddling the ridge with the inner basin to the east and cinder cones of the San Francisco Volcanic Field to the west. We got to spend more summit time than usual because of the great weather: sunny, pleasant and no winds! A jubilant group arrived with one South Carolina couple that had Humphreys on their peak list. We made a hasty retreat down the trail in anticipation of our celebratory beer. We walked around a vibrant Flagstaff downtown, after leaving our car at the hotel. Afterward, we met our Uber driver in front of an impressive climbing gym.
For the Geo-Curious: San Francisco Volcanic Field
Humphreys Peak sits in the middle of Northern Arizona's San Francisco Volcanic Field, which covers about 1,800 square miles. Around 600 volcanoes were produced in this field starting 6 million years ago. Many of the mountains between Flagstaff and the Grand Canyon represent this field. These eruptions "migrated" west to east, meaning the eastern eruptions were the youngest. What better place, besides a helicopter or plane, to see a lot of these volcanoes than the summit of Humphreys? Volcanism is usually associated with tectonic plate boundaries, like with Mount St. Helens or Mount Rainier or Kilauea in Hawaii. This volcanic field occurs on the border of the Colorado Plateau and the actively stretching (extensional) Great Basin and Range Province. Stretching causes a thinning of the Earth's crust, which in turn brings warm mantle rock closer to the surface. The resultant depressurization and increased heat of this rock was the impetus for the San Francisco Volcanic Field and its many volcanoes. Volcanic rock color gives a clue as to what type it is. The more silica it contains, the lighter and thicker (more viscosity) it is. Basalt is black and has the lowest amount of silica, with larger amounts of iron and magnesium, and is the most prominent rock making up the San Francisco Volcanic Field's volcanoes. Andesite, a dark grey rock, has an intermediate silica amount, and is the prominent rock of Humphreys and Aggasiz Peaks. Light grey rhyolite is the most silica-rich rock and therefore is more viscous.
Picture Canyon and the Northern Sinagua Petroglyphs
Long before Flagstaff's vibrant downtown, the Sinagua (sin = without, agua = water) people inhabited northern Arizona between 500 - 1450 AD. They were hunters and gatherers with some agricultural practices. We stopped by Picture Canyon Natural and Cultural Preserve in Flagstaff to find the Northern Sinagua petroglyphs, one of which is a waterbird. We found this cluster of petroglyphs on basalt boulders along the Tom Moody Trail, next to Rio de Flag, a permanent stream, where perhaps the Sinagua saw cranes or herons. The "zig-zag" petroglyph may represent lightning, water, or mountains. Check out photos of these petroglyphs at the end of this post. A 1.5-mile section of the Arizona Trail treks through this preserve.
More to Explore
As usual, with each hike we do, we find more to do, more places to explore. We're in our early 60's, gratefully healthy, and trying to get as many summits and expeditions in as possible before we can't. We've lost a little speed, joints hurt a little more from our earlier hiking days, but we still take advantage of our good health and keep challenging ourselves. Life is short - get out there (put the phone away) for mind, body and spirit!
From the Snowbowl trailhead, hike up this ski slope and then enter the forest. Humphreys summit is in the shadow.
Switchbacks through a beautiful forest to saddle on ridge.
Reach Humphreys' south ridge at 3.8 miles and 11,780'. Looking toward the east at the "Inner Basin" created by a massive avalanche. Humphreys Peak trail traverses along ridgeline upper left. The green peaks lower center may be Aubineau and Rees on the northern-most rim of the Inner Basin.
Intersection at saddle. A glimpse of the top of Arizona Snowbowl's gondola just above the bottom sign. No hiking off-trail probably due to protection for the threatened San Francisco Peaks groundsel.
On the ridge headed up to Point 12,297', the second "bump" from the left.
Heading north up the ridge from the saddle. Trail markers are made of old branch signs. Also a warning sign to stay on the trail.
Looking back at Agassiz Peak on the left and Arizona Snowbowl Ski Area in valley to the right.
Approaching Humphreys' summit.
Humphreys' summit!!
Someone made two rock lounge chairs on the summit.
Heading back: Agassiz Peak on the left.
Looking west toward Kendrick Peak (my best guess after looking at maps of the San Francisco Volcanic Field map).
Map of San Francisco Volcanic Field from Aperiodic Wanderings
Humphreys Peak is the largest in the center with its horseshoe-shaped Inner Basin on the east side sculpted by a giant avalanche from a caldera collapse. 
Off the saddle and into the forest on the way back down.
Our GPX tracks on Google Earth.
Caltopo map of our tracks (in pink) going through switchbacks and along ridge to Humphreys summit.
This map includes all six of the peaks surrounding the "Inner Basin." Profile of Humphrey ascent from 9,266' to 12,629' in 4.8 miles.
Interactive Caltopo map of the San Francisco Peaks and Flagstaff Area with our GPS tracks.
Northern Sinagua petroglyphs. Note the waterbird (first photo) in lower center, partially shaded.
Sources
Atlas Obscura. Picture Canyon. Wade, B. (from Arizona Snowbowl website). San Francisco Peaks Geology. Cook, T., Abbott, L. 2017. Travels in Geology: Cones and Craters in Flagstaff, Arizona. From website Earth. USGS. San Francisco Volcanic Field. The University of Arizona: Arizona Geological Survey. San Francisco Peaks Inner Basin.
2 Comments
11/15/2024 04:32:27 pm
You really scraped the sky on this one. I'd never heard of volcanism caused by stretching/thinning of the crust. That's fascinating. 11/15/2024 05:42:31 pm
I like your term "scraped the sky"! Leave a Reply. |
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Sue and Fred
About this blogExploration documentaries – "explorumentaries" list trip stats and highlights of each hike or bike ride, often with some interesting history or geology. Years ago, I wrote these for friends and family to let them know what my husband, Fred and I were up to on weekends, and also to showcase the incredible land of the west.
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