Marcus Landslide, McDowell Sonoran Preserve: Tom's Thumb Trailhead, Phoenix - Scottsdale - Mesa, Arizona
Marcus Landslide - 3.0 miles
McDowell Sonoran Preserve: Tom's Thumb Trailhead
|Round-Trip Length:||3.0 miles (to landslide)|
|Start-End Elevation:||2,795' - 2,555' (2,795' max elevation)|
|Elevation Change:||-240' net elevation loss (+378' total roundtrip elevation gain)|
Marcus Landslide - 3.0 Miles Round-Trip
The Marcus Landslide Trail runs along the east edge of McDowell Sonoran Preserve to a massive landslide that scientists believe occurred 500,000 years ago. An estimated 194 M cubic feet of rock and vegetation slid off the side of East End Peak, the second largest known occurrence in Arizona.
It carried 25.8 billion pounds of debris that topped 44 mph down the mountainside before settling about a mile from the initiation zone. Energy released by the slide is thought comparable to an atomic bomb in an event that may have only lasted a few minutes.
This process accounts for the large, spherical boulders and formations found across the landscape.
Granite further breaks down into Grus, a course grain fragment the size of sand or small pebbles that can act like ball bearings on a slope. Granite may also erode into clay, which contracts when dry and expands when wet.
Expanding clay and rounded grus particles create a slippery surface, which set the stage for massive instabilities on steep slope - like that of East End Peak.
500,000 years ago the local climate was much cooler and wetter than today. Freeze-thaw cycles weakened perpendicular joints in granite rock masses and hastened erosion.
Coupled with steep slopes and a trigger event – like heavy rain or an earthquake – a major landslide became possible.
The Marcus Landslide Trail runs 1.5 miles south from Tom’s Thumb Trailhead to the slide area, and continues on a one mile loop through the heart of the impact zone. Mild grades and a smooth grus track are ideal for families, runners and cyclists.
While the landslide is the trail’s main attraction, mushroom-shaped rocks and the bajada itself are compelling reasons to visit.
Mushroom formations start their lifecycle as underground rectangular blocks of granite. Perpendicular fractures in these blocks expose corners to accelerated erosion, while flat surfaces break down at a slower rate.
The difference produces rounded shapes that are further exaggerated as subterranean rock is exposed to water for longer periods of time.
The net result is a large, rounded cap with a narrow base – or mushroom. You’ll see mushroom formations in various states of their lifecycle all along the trail. Large plots of well-spaced brush, trees and cholla complement this extraordinary geologic setting.
- N33 41.666 W111 48.082 — 0.0 miles : Marcus Landslide Trailhead
- N33 41.640 W111 47.810 — .3 miles : Feldspar Trail split
- N33 41.672 W111 47.686 — .4 miles : Caballo Trail split
- N33 41.407 W111 47.318 — 1.0 miles : Rolling travel across bajada
- N33 41.154 W111 47.253 — 1.35 miles : Mushroom rock exhibit
- N33 41.057 W111 47.257 — 1.5 miles : Marcus Landslide
- Mild grades and smooth surfaces are ideal for running and biking. Several trail connections lead into McDowell Mountain Regional Park for extended travel options.
The landslide is named after Dr. Melvin Marcus, a geography professor at ASU and accomplished alpinist, academic and mentor.
Bees are active in this area. Remain on designated trails at all times to avoid negative encounters.
Rules and Regulations
- Dogs must be on a hand held leash at all times.
Directions to Trailhead
Tom's Thumb Trailhead is located on the northeast side of McDowell Sonoran Preserve.
This newly renovated and expanded trailhead is located 11.9 miles from HWY 101 on McDowell Mountain Ranch Road.
From Highway 101, take the Pima Road Exit (#36) and head 4.7 miles east on Pima to Happy Valley Road. Turn right on Happy Valley for 4.5 miles to McDowell Mountain Ranch Road. Follow signs (right) for Tom's Thumb Trailhead.
McDowell Sonoran Conservancy 16435 N Scottsdale Rd. Suite 110 Scottsdale AZ, 85254 480.998.7971