Feldspar Loop Trail, McDowell Sonoran Preserve: Tom's Thumb Trailhead, Phoenix - Scottsdale - Mesa, Arizona
Feldspar Loop Trail - 1.5 miles
McDowell Sonoran Preserve: Tom's Thumb Trailhead
|Round-Trip Length:||1.5 miles|
|Start-End Elevation:||2,795' - 2,958' (max elevation)|
|Elevation Change:||+163' net elevation gain (+212' total roundtrip elevation gain)|
Feldspar Loop Trail - 1.5 Miles Round-Trip
The Feldspar Trail makes a short loop through the eastern bajadas and granite rock formations of McDowell Sonoran Preserve. It offers a compact introduction to the area's unique geology, climbing access and trail extensions for Marcus Landslide, Tom's Thumb and McDowell Mt Regional Park.
About 1.4 million years ago, rising magma intruded overlying rhyolite and quartzite rock layers and lithified into granite. Granite masses can fracture into perpendicular joints, exposing square edges that become rounded through erosion.
Flat surfaces break down slower than exposed edges; the difference produces rounded shapes that can be 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 at various points of their geologic lifecycle along this trail.
Looking east, the lower Verde River Basin separates the McDowell Mountains from the Four Peaks and Superstition Mountains. The Verde River originates southwest of Flagstaff and flows 195 miles into the Salt River east of Fountain Hills.
The Verde River is one of the oldest rivers in Arizona. It was born after an upstream lake overflowed into the basin, which formed 12-18 million years ago as parallel mountain ranges were pulled apart.
While granite rocks with a distinct Joshua Tree feel are the main attraction, the bajada itself is equally compelling. Water funnels quickly from steep slopes into the bajada, enabling vegetation to thrive.
- N33 41.670 W111 48.089 — 0.0 miles : Marcus Landslide Trailhead
- N33 41.638 W111 47.810 — .3 miles : Feldspar Trail split
- N33 41.428 W111 47.993 — .65 miles : Climbing access spur
- N33 41.429 W111 48.012 — .75 miles : Mesquite Trail split
- N33 41.356 W111 48.323 — 1.1 miles : Tom's Thumb Trail split
- N33 41.636 W111 48.132 — 1.5 miles : Tom's Thumb Trailhead
- Feldspar is a common mineral occurring in igneous rocks that sometimes erodes out and becomes incorporated into sedimentary rocks. Feldspar is the most common mineral in the world.
- Those with time should consider continuing a short distance on the Marcus Landslide Trail, which leads to a massive landslide that occurred 500,000 years ago.
An estimated 194 million 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.
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