Rock City at Mt. Diablo State Park: Adventure through Time

Looking for a unique Bay Area adventure? Or maybe just a new place where the kids can burn off some energy? Make sure to add Rock City, in Mt. Diablo State Park to your list! 

Rock City is part of an uplifted rock formation that extends along the southern side of Mount Diablo. The sandstone rocks that you’ll soon be crawling over, under, and through have been shaped by water, wind, and time over millions of years. What you’ll find today is a series of small caves and tunnels that kids of all ages love to explore. 

IN THIS POST:

PLAN YOUR VISIT

Always check the official Mount Diablo State Park site for the latest updates related to Covid-19 safety guidance and park conditions. This is a popular area. If you’re going on a weekend, try to get there early to avoid parking troubles and dealing with crowded trails.

  • Entrance Fee: $10
  • Hours: 8am – Sunset
  • Dog Friendly: Dogs NOT permitted on trails, fire roads or in park buildings.
  • Stroller Friendly: East Fossil Ridge Road and the road to Artist Point Picnic Area were wide access roads that could be navigable with an off-road stroller. Popular rock formations like Elephant Rock are near South Gate Road and a quick walk from the car. The trails through the wind caves and to Sentinel Rock are not stroller friendly.
  • Restrooms: There are three restrooms located in the Rock City Area: Lower Rock City Picnic Area, Elephant Rock picnic area, and Live Oak Campground. At the time of writing, all water has been turned off in the area due to a water shortage. Bathrooms were not functioning during our visit, but mobile toilets had been added next to the restroom in the Lower Rock City Picnic Area.
  • Park Features: Massive rocks for scrambling, Wind Caves for exploring, Hiking trails with expansive views over the valley below, Picnic areas, Camping

HOW TO GET TO ROCK CITY, MT. DIABLO

  • Main Entrance: Enter Mount Diablo State Park through the South Gate Entrance. The address is: 2675 Mt. Diablo Scenic Boulevard, Blackhawk, 94506. The drive to the gate alone is an adventure!  There are a few pull out areas where you can pause to enjoy the stunning views over the valley below.
  • Parking: You’ll see signs for Rock City on your right shortly past the South Gate Entrance of Mount Diablo State Park. The first parking lot is small and fills up quickly on the weekends. If it’s full, keep going! You’ll find a few more spots along South Gate Road and at each picnic area throughout Rock City.

ROCK CITY, MT. DIABLO MAPS

Photographed area map of trails, picnic areas, and landmarks taken onsite.

THINGS TO DO AT MT. DIABLO’S ROCK CITY

EXPLORE THE WIND CAVES

Rock City Wind cave structure

These hollowed-out caves are perfect for exploring with young kids and are what most people think of when they hear about Rock City.  Start your Wind Cave exploration near the Big Rock picnic area. You can follow part of the “Trail through Time” from here, or just have fun wandering and looking for the next best caves to explore. 

Information signs told us that the Wind Caves were not formed by wind so much as a type of erosion led by rain mixed with carbon dioxide. This mixture formed weak acidic water that ran into the rock dissolving the “glue” that held the grains of the sandstone together. As the rocks’ crust fell away over time, the weakly glued sandstone was exposed to the elements and eroded more quickly than the outer parts of the rock. Think of it as nature’s way of sculpting rocks over time.  Sadly, you can see that visitors have added their own ink and carvings in more recent times. 

As you can see from the photo of the area map, this area has plenty of interchangeable trails to explore whether or not you have a destination in mind. During our visit, we started following the Wind Caves from Big Rock Picnic Area, headed toward the CCC Trail that leads to Sentinel Rock, looped back to the Summit Trail and Wall Point Road, and found Big Rock last.

ELEPHANT ROCK

Photo of the landmark rock described as elephant rock.
Elephant Rock (Photo Credit: waymarking.com)

Easily accessible, Elephant Rock is located right off South Gate Road, near the turnoff to the Live Oak Campground.  It even has its own picnic area nearby. 

You won’t believe this, but we missed Elephant Rock! It was a classic case of me looking for hiking trails and missing what was right in front of us. In this area, it’s helpful to remember that there isn’t one exact trail that is going to take you through the Rock City highlights. This is a place to explore as you go. Take it from me, just keep your eyes open and enjoy the present.

PICNIC AREAS

Rock City picnic area in the grotto. Even the BBQ is constructed out of rocks
the boys made slides out of the rocks near our picnic area in the Grotto

One thing I love about Rock City, and Mt. Diablo in general, is the unique picnic areas. We enjoyed snack time in the Grotto Picnic Area shown here. It was one of the coolest park picnic areas we’ve experienced! The grill is set in rocks, and the boys climbed the nearby boulders as soon as that last bit of applesauce was slurped. They even turned some of the smooth rocks nearby into a slide!  There were plenty of interesting picnic spots throughout the Rock City area. If you’re looking for a scenic and fun place to grill out with your family, look no further. We’ll definitely plan to stay longer next time we go.

CAMPING

If you’d prefer to explore Rock City without the crowds, consider extending your day trip into a campout. Live Oak Campground is one of Mount Diablo’s three main campgrounds, and located smack dab in the middle of Rock City. Each site has a fire grill, picnic table, and raccoon box to help keep the critters away. Reviews are mixed on their effectiveness though!

Be aware that the sites are pretty snug. Campsites 10 through 16 seem to offer the most seclusion. Alcohol is not allowed in the park, even in campsites, so keep that in mind if you like to enjoy a beer by the campfire at the end of the day.

ROCK CITY HIKING TRAILS

SENTINEL ROCK

John looking out toward Sentinel Rock

Hiking to Sentinel Rock is one of the most popular things to do in Mount Diablo State Park, and yet it’s still a bit confusing to navigate. As long as you can keep your bearings, it’s ok to veer off the trail here and there.

As you can see in the area map above, there are a few different ways to get there.  Using terminology from the area map in this post, the 1.2-mile loop starts at Elephant Rock and heads toward Sentinel Rock along the Elephant Rock Trail. The trail will bring you to the base of the rock itself. The base area can seem like a maze to first-timers, but keep circling east until you see the steps carved out by the Civilian Conservation Corps. Hikers can summit the rock using the steps and cables provided.

Many find this steep climb challenging. It’s above our skill level, but others have felt comfortable bringing children as young as 6. Be prepared to assist children. 

After reaching the top of the rock, hikers will loop around onto the Summit Trail. Follow Wall Point Road to head back to Rock City. Cut through the Wind Cave section of Rock City on your way back to the Elephant Rock Trailhead. 

There is a shorter path to Sentinel Rock via Live Oak Campground. Park in the picnic area and pick up the trail behind campsite 20.

TRAIL THROUGH TIME

Playing in a Manzanita tree tunnel on the Trail Through Time

One of the unique qualities of Mount Diablo is that the mountain formed from a mass of rock that was gradually forced up through the earth’s surface. You encounter older and older rocks as you climb. Each tells a story of previous landscapes, climates, and life forms. 

The Trail through Time was developed to share the story of these rocks, which together represent the entire geologic history of the Bay Area. The trail spans 6.3 miles from the top to the bottom of Mount Diablo. The oldest rocks are 190 million years old and the youngest rocks are 10 million years or younger.  We decided to follow the portion of the Trail through Time that winds through Rock City and stopped to read the interpretive panels along the way. Though I’m still working to understand all of the geology we passed through, it was enough to fire up our imaginations and got us thinking about the plants and animals that might have stood in that very spot before us. 

We started by the short loop that began at the Big Rock Picnic Area and followed past a large structure of Wind Caves. Soon after, we took a short detour on the CCC Trail to Sentinel Rock Overlook and then headed back along the Trail through Time to the Summit Trail. Finally, we caught Wall Point Road and looped back to the Grotto Picnic Area for a snack break and more Wind Cave exploration.

WHY WE LOVE IT

Posing for the camera in a shallow wind cave
There are also plenty of open landscapes for the boys to jump and run around

Rock City is the kind of place that is easily accessible and yet feels like a great adventure. It’s a bit confusing to get your bearings at first, but it’s also just a cool place to explore without an agenda. Once we let that sink in, we basically let the boys explore until they were tired and called it an excellent day. We’re looking forward to our next visit to Mount Diablo!

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