Mount Diablo State Park rises dramatically from the Walnut Creek area in Contra Costa County, impossible to miss once you’re driving through the region. This 3,849-foot mountain has played a significant role in California’s history since 1851, when it was established as the initial point for the Mount Diablo Base Line and Meridian—the reference system used for land surveys covering two-thirds of California and all of Nevada. From the summit, you get expansive views across the Bay Area and beyond, stretching all the way to the Sierra Nevada on clear days.

The park itself covers over 20,000 acres with plenty of hiking and biking trails winding through oak woodlands and grasslands. Dogs can’t join you on those trails or fire roads, which is worth knowing upfront if you were hoping for a lengthy backcountry adventure. What you can do with your dog is explore the campground and developed areas like picnic grounds, making it feasible for a day visit or overnight stay. The visitors center provides good information about what’s happening in the park, though dogs aren’t allowed inside the buildings.

If you’re camping, your dog needs to stay leashed during daylight hours and be secured either in an enclosed vehicle or tent once night falls. The campground itself sits at a decent elevation, so mornings can be cool even in summer. Picnic areas scattered throughout the park give you spots to sit with your dog while taking in views of the surrounding landscape—less strenuous than hiking but still a nice way to spend time outdoors together. The park gets busy on weekends, particularly in spring when wildflowers are blooming, so arriving early helps with parking and finding quieter picnic spots.