Lake Marie Loop via Skyline Trail and Manzanita Trail is a 6.6 mile loop trail located near Napa, CA that features beautiful wild flowers and is rated as moderate. The trail offers a number of activity options and is accessible year-round. Horses are also able to use this trail.
Park at the staging area at the end of 4th St.
I hiked at May 25. The weather was gorgeous.
This is a very easy and accessible trail from the Skyline State Park entrance. You still have to pay for day use, but it's worth supporting the California state parks. There are several trails that you can get to the lake. The easiest would be to just take the road out and back. However, if you try the upper or lower lake trail at the junction split it is worth the view. Watch out for mt bikers though, they seem to love this for a quick out and back "town" ride. One point of interest is the Giant Fig tree. You can find a very small trail leading into the tree, but you need to check it out.
We hiked this trail a couple days after some heavy rain. The mud can get really slippery. I would recommend hiking the trail more than a few days after heavy rains. The first mile starts off with switchbacks and an elevation gain of about 600 feet. The rest of the trail is pretty flat.
Lake Marie is really a glorified man made pond, so you're not missing anything there. The trails are well maintained despite the rain and the views of Napa are great. The Marie Road is a gradual descending trail the whole way back. It takes about 45 minutes to return. Full loop about 3 hours.