The dog-friendly Pena Adobe Hill trail is a 3.2-mile out-and-back hike in Pena Adobe/Lagoon Valley Park, conveniently positioned just off Interstate 80 between Vacaville and Fairfield. This moderately difficult route climbs through cattle grazing areas and rewards you with expansive views of the surrounding hills and the lake below. Dogs are welcome throughout, and you’ll find sections where they’re permitted to roam off-leash, which makes for a more relaxed outing if your dog has solid recall.

The trail operates year-round, though timing matters depending on what you want from the experience. During rainy season the path gets muddy and can be slick in spots, so watch your footing and your dog’s too. Spring is the real showstopper here—the rolling hills turn a rich green and California poppies dot the landscape in scattered patches of orange and gold. It’s worth planning a trip for that season if you can.

Getting to the trailhead takes a bit of navigation within the park. Drive through the yellow gate to reach the main parking area and pay the parking fee at the kiosk. From there, head toward the main road on the opposite side of the lake from where you parked—that’s where the trailhead begins. The positioning means you’re essentially starting from the far side of the lake, which gives the hike a different character than many nearby trails.

The moderate difficulty rating is accurate—it’s not a walk around the block, but it’s not a grueling scramble either. The elevation gain is real, but the payoff in views and the chance to let your dog stretch their legs in a more open setting makes it worth the effort. Come midweek if possible to avoid weekend crowds, and bring extra water since shade is minimal once you get moving uphill.