Wandering Around Inside a Volcano: Exploring Pinnacles National Monument

Pinnacles National Monument in the California Coast Ranges is one of the most beautiful parks no one has heard of. Far from any major population centers, it just doesn't get the visitation or attention of the better-known parks of the Sierra Nevada or the California coast. It's an interesting place to hike on the basis of scenery alone, but it also has an extraordinary geological story. To explore the park is to wander about inside a volcano.

The Pinnacles volcano is a composite of five or so rhyolite cones that were erupted around 23 million years ago. The flanks of the volcano were coated with rhyolite breccia from mudflows as well as rhyolite lava flows, pumice, and a bit of andesite and dacite. The intricately eroded towers contrast strongly with the more muted topography of other parts of the Coast Ranges.

The park was established in 1908 for the unique scenery, but in the 1970s an extraordinary discovery was made: half the volcano was missing, and the missing half was on the other side of the San Andreas fault...195 miles away in Southern California! Pinnacles turned out to be an important piercing point of the fault and is critical in understanding the nature of the San Andreas fault system. I discussed this in an earlier post that included a map showing the offset (click here to see it).

The High Peaks are mostly composed of the breccia unit. A network of trails surround the ridge and cross over the summit. In places, steps are carved directly out of the rock, and a few cliffs required the use of bridges which were more or less nailed to the cliff.

On our recent field class, I gave the students a bit of free time to explore the talus caves (surprisingly long and dark), and took off for the High Peaks Trail to catch a bit of the sunset. The previous day a storm had come through, and another was due in a few hours. In the meantime, the sky was full of puffy clouds that nicely caught the rays of the setting sun.

I covered the four miles in an hour and a half (gotta get back to the gym, huff...puff...), but I had a great time walking through the inside of the volcano. I lingered a bit at the small reservoir looking at the reflections, and then fairly ran down the trail to meet my waiting students.

Rhyolite in the California Coast Ranges? And Happy Thanksgiving...

I only provided one picture of Pinnacles National Monument in California's Coast Ranges in my previous post, and it showed none of the scenery that makes the park a special place. So here are two views of the 22 million-year-old rhyolite composite volcano that was erupted, sliced in half by the San Andreas fault, faulted into a graben structure, exhumed by uplift, and eroded by water and wind and mass-wasting into a beautiful parkland.

The first photo is a view from the High Peaks Trail, a marvelous 5 mile loop through the heart of the park. The walk across the ridgeline is just stunning. In many places, footholds had to be scooped out of the rock to provide access, although the exposure level is not too frightening (nothing like Angels Landing in Zion, for instance). On a clear day, the far ridges extend forever into the distance, while the giant monoliths of rhyolite dominate the foreground. This hike, along with the trail to Delicate Arch, and the climb of Angels Landing, is one of my favorite hikes in the world.

The second shot is a view of the previously mentioned high peaks from the perspective of the south end of the park on the trail to the Chalone Peaks. The High Peaks Trail winds along the spine of the ridge in the center of the photo, and has connecting points to trailheads on both sides of the park (no roads cross the park, so one must choose to visit from the west or the east side).

The third photo is one of the wild denizens of the park, an old Tom Turkey. I have a feeling this bird would have issues with a certain recent vice-presidential candidate. I have seen a lot of wildlife in the park, include a huge flock of wild turkeys, four or five California Condors, huge numbers of woodpeckers, the standard deer and various rodents, and my favorite, a huge bobcat. The cat was hanging out near the edge of the campground near the road, and as we approached on the highway, what I thought was a feral kitty-cat seemed to grow larger and larger until I finally realized what it was and grabbed for my camera. Too late of course. And I can't help but look for the cat at the same spot every time I pass by during subsequent trips, camera ready in hand.

I hope everyone in the geoblogosphere has a fine Thanksgiving, even if you are not in the particular country that celebrates the day. Times are toughening up for many of us, but here's wishing that we all weather the storm, and that the job situation brightens for those of you who are between jobs and searching for employment. Best wishes to all of you.