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.

Trail Map | Photo Gallery

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.

Granite rock in this area formed as magma intruded overlying rock and lithified. Granite masses can fracture into perpendicular joints, exposing square edges that become rounded through erosion.

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.