The Arch Canyon Trail is a great short hike combined with a scenic loop drive that ventures far back into remote canyons of the Ajo Mountains on the eastern edge of Organ Pipe Cactus National Monument. While the access road is gravel, it is well-maintained and even paved on the steepest parts, so it is accessible by nearly any vehicle. It is also one-way for most of the loop, so driving it is no so stressful.
Mount Ajo rises nearly 4,000 feet over the desert floor. This small range exhibits a variety of plant zones, from the pure Sonoran Desert at the lowest elevations to a more oak-juniper scrub environment a little higher. The road winds around bluffs and smaller mountains and is constantly flanked by saguaro and organ pipe cactus in all of their interesting forms. There is a small picnic area with shade at milepost 7. At the trailhead just past milepost 10, there is no shade, but there are a number of informational displays describing the geology of the area and how the arch was formed.
The arch itself is best viewed a short way up the trail, and the easy part of the trail is 0.75 miles one-way. For the hardy, it is possible to scramble up loose rocks and switchbacks to a view of the arch about 1.25 miles in. The arch is about a half-mile away from the trailhead so it looks small, but it actually measures over 700-feet long and 36-feet high. It was formed by the successive freezing and thawing of water amid cracks in the rocks, and it is actually a double arch with a small opening above the main arch.
Bird life is abundant in the canyon, with cactus wren, quail and owls sometimes visible. The view of the surrounding canyon walls is impressive, as is the extreme quiet that is evident everywhere in Organ Pipe Cactus National Monument. This area is far from any air corridors or military bases, so planes are rare.
Back at the trailhead, the scenic loop drive continues for another 12 miles and offers more spectacular views, particularly at sunset. There is another strenuous 6-mile loop hiking trail that goes to Bull Pasture and Estes Canyon, and the trailhead parking is just a few miles past the Arch Canyon parking area.