Sombrero Peak - West Approach Trail is a 10 mile out and back trail located near Boulevard, CA and is rated as moderate. The trail is primarily used for hiking and is accessible from October until May.
The summit views are terrific once you figure out which chute gets you up the rocks. Most of the chutes on west and northwest sides of the summit are frightening in boots with a pack; maybe with rock-climbing shoes but down climbing from there is needlessly risky. Go around to the north side of the summit and there's a more low-angle chute with manageable blocks. There's no water and no trees for shade, so bring at least 3 liters water and have a good hat and sunblock. Give yourself about 7 hours out and back, more if you make lots of stops.
The trail to the base of Sombrero is pretty straightforward. Park at the Cottonwood campsite off McCain Valley Road and find the trail head. The five mile trek to the base of Sombrero is a combination of pretty standard trail, a poorly maintained road, and a dirt bike trail. There is no trail on the mountain itself. Just a scramble up a surface of loose decomposed granite offering poor footing, with boulders to circumnavigate or climb over. The last hundred feet or so to the summit on this west approach are terrifying unless you are an experienced climber.