Not a bad man made trail. We did a total of 7 miles. Very wide gravel trail with some great views if you follow the whole trail. Also good for winter due to gravel and did not have a any problems even when it rained on us for about a mile of the walk.
Great park with free parking (can get busy) and awesome scenic view of Napa River and wildlife's along the wetlands. Lots of opportunities for bird watching. It's mostly a gravel trail, flat with little to no shade. There is a nice breeze since you're near a body of water. The sun sets behind the mountains across the bay which makes for a nice photo. The mosquitoes are active as the sets so bring a bug spray. There is a portable toilet in the parking lot and plenty of benches and tables. On June 23, 2016 we walked a 3.7 mile loop.
Laura S. on Napa River and Bay Trail
Great for the early morning walk with your dog!