Glen Canyon & O’Shaughnessy Hollow

and O’Shaughnessy Hollow

Glen Canyon (and O’Shaughnessy Hollow) is one of the southern most parks within the San Francisco city limits and was one of the last few on Chris and my ever-dwindling list. Glen Canyon Park occupies about 70 acres along a deep canyon adjacent to the Diamond Heights and Miraloma Park neighborhoods and is full of trails. O’Shaughnessy Hollow is a rugged, undeveloped 3.6 acres tract of parkland that lies immediately to the west with no trails. Together they make one giant park.

Last Sunday we invited our fellow hikers Michael, Kyle, and Ichigo to take on Glen Canyon with us. We had a large brunch at our place and then started walking. The majority of our trip was along O’Shaughnessy Boulevard down the west side of O’Shaughnessy Hollow. The northern most part of the park is taken up by San Francisco School of the Arts.

San Francisco School of the Arts track and football field.

We entered the park through Bosworth St. At the entrance to the park there was a recreation center and run down looking preschool. Overall it looked like your average New England park.

Average NE park: flat, trees and dead leaves.


The park’s history commences with Adolph Sutro’s (that guy again!) purchase in the 1850s of 76 acres of the canyon, which he named “Gum Tree Ranch” after the blue gum eucalyptus trees he had planted. The first commercial manufacturing of dynamite in the U.S. occurred in the canyon; on March 19, 1868, the Giant Powder Company began production at its first manufacturing plant. The factory did not last long. On November 26, 1869, an explosion completely destroyed the entire facility, turning every one of the buildings on the place, and the surrounding fencing, into “hundreds of pieces”.

In 1889 Crocker Real Estate Company installed a mini-amusement park with an aviary, a mini-zoo–bears, elephants and monkeys, a bowling alley, and, for extra thrills, hot-air balloon rides, and an intrepid tight-rope walker who performed on a wire stretched across the canyon. Unfortunately it was the site of many boisterous drinking brawls and in 1922, the city bought Glen Canyon Park and Recreation site and made it into the park we have today.

After traveling north for a little while we came upon a steep incline covered in rocky outcroppings.

Rocky outcroppings.


The scenery of Glen Canyon Park is distinguished by numerous large outcrops of rock. The most striking of these consist of reddish, layered “Franciscan” chert. The bedrock of the canyon is made up of rocks of the Marin Headlands terrane, which is a large packet of rock that extends diagonally from the Marin Headlands, through the Twin Peaks and Glen Canyon area, and on to the southeast. This terrane is from 100 to 200 million years old (i.e. the Cretaceous and Jurassic periods).

The bedrock of the lower slopes of the canyon – largely hidden under slope debris/ravine fill – is pillow lava or greenstone; these erupted from fissures in the deep ocean floor when the terrane was located hundreds of miles southwest of its present location. The upper slopes and cliffs are of layered chert, which hardened into rock from the ooze of remains of countless radiolarian creatures that accumulated on top of the lava. The ooze was colored red by iron from hydrothermal springs. Both lava and chert were formed in the deep ocean near the equator, and were rafted northeast on the gradually-moving ocean floor toward California.

Big arms!

More rocky outcroppings.

The rocks were really fun to hike around on and are apparently well-known to SF’s experienced rock climbers. Our northbound trail lead us to a steep, tiny path that cut into the western ledge of the canyon. The trail is only about a foot in width with a sharp incline and decline on either side. At one point a pregnant woman was hiking from the other direction and I almost lost my footing trying to get out of her way.

Heading out onto the tiny, steep path.

The path lead us around the northernmost part of the park and back around into the canyon. At the very bottom there were metal grates were we could hear running water, but we didn’t see any signs of the Islais Creek that supposedly starts there. At the center of the canyon, there’s a small, rocky hill that you can climb up on.

Even more rocky outcroppings.

Ichigo: King of the Rocks.

After we hung out on the rocky hill for a bit and Michael made a few prank texts (poor Grayden), we made our way up the steep western edge and exited the park on Turquoise Way.

Goodbye Glen Canyon and O’Shaughnessy Hollow!

Overall the trip down there wasn’t as bad as I had expected (takes about an hour from our place) and the park is well worth it. There are a bunch of trails and you can see the whole park in 2 hours or less. I recommend hiking shoes if you’re planning on going as there are lots of sandy dirt inclines and, obviously, rocks. Lots of people bring their dogs. It says at the entrance that it’s a leash only park, but none of the dogs (besides Ichigo) were wearing theirs. If you’d like to see all of my pictures from Glen Canyon Park, per usual – check out my flickr set.

Until next time,