The Thylenanti loop combines three connected trails—Thylenanti Trail, Lagoon Tower Road, and Jepson Loop Trail—to create a solid 6-mile moderately difficult circuit through Pena Adobe/Lagoon Valley Park in Vacaville. This is one of those trails that attracts everyone: hikers, mountain bikers, and dogs, especially on weekends, so don’t expect solitude if you’re going on a Saturday afternoon.

Start from the first parking lot before the dog park area. Your dog needs to stay leashed throughout, and there’s a parking fee, so bring cash or check what payment methods they accept. The trail loops around the park’s perimeter, passing through open grassland where cattle often graze. This is actually worth knowing because while the cows generally ignore hikers, keeping your dog close on leash is the responsible move and honestly makes the whole experience less stressful for everyone.

The lack of shade is real here. In summer, the exposed terrain means midday heat reflects off the grass, and your dog can overheat quickly. I’d strongly recommend starting early—think sunrise to mid-morning—especially during warm months. Bring more water than you think you’ll need. A collapsible bowl takes up almost no pack space and makes it easy to give your dog a drink at any point along the route.

The terrain itself is manageable but rolling enough to keep things interesting. You’ll get views across the valley, and the moderately difficult rating is honest—it’s not grueling, but it’s a real workout, not a casual stroll. On a clear day the views make the effort worthwhile. The main trade-off here is dealing with crowds and limited shade versus getting in a good long walk with varied scenery. If you can swing a weekday visit or an early weekend start, you’ll have a much better experience.