One of the most beautiful areas for hiking that is a day trip from Fresno in the Bay Area near Calistoga is the Oat Hill Mine Trail. The hiking trail area is actually 4 hiking trails which are all connected. One can start at the Table Rock hiking trail which is about 3 miles of hiking through forests. The trail ends at a beautiful viewing point where it connects to the Palisades hiking trail which is about 4 miles. This hiking trail then connects to Oak Hill Mine road hiking trail which is about 4.5 miles. The Oak Hill Mine connects to both the Highway 29 hiking trail and also the Silverado hiking trail. All of these hiking trails start or end in the Robert Luis Stevenson State Park. You can park on the east side just off of Highway 29 for easy access to the hiking trailhead. Regardless of how long of a hike you take make sure to bring water and sunscreen. Although much of the hiking is in forested areas but there are several sections with no shade or minimal shade. Additionally despite being located in the Bay Area it can get hot on the trails.
When you start at the Table Rock hiking trail you will climb up quickly through pine trees and manzanitas. Keep your eyes open because through the forest you can often see views of Mt St Helena which is to the north of the hiking trail. About 5 miles in along the trail is a beautiful rock area with unusual rock formations and views of Middletown which is to the northeast. You can also see Point Reyes to the south and east on a clear day. After hiking up a bit more you can see amazing views of Napa Valley to the south of the hiking trail. Just past this the hiking trail becomes a bit technical. There are several areas with off stacked rocks so you have to boulder up the rocks a bit. The rocks can be a bit slippery and times and are not always the most stable thing you have ever walked on.
After you pass the bouldering section the hiking path gets much easier. You begin to see a multitude of wildflowers and enjoy a relatively flat area.
If you continue you may pass a multitude of Miner's Lettuce and many other beautiful wild plants and flowers. You do need to be careful because there are some areas that I have seen Poison Oak in. As you continue hiking further you reach another rocky area. The rocky area is not always very stable and is a bit of a spiral so be careful as you are hiking in this area.
Some of the amazing scenery you will see are mountains, peaks, circle rock formations, the Bay Area residential areas, California poppies, fiddleneck, money flower, lupine, and strange stacked roads.
One tip from experience is to start very early if you plan to go the full length of the trail. One way it takes about 7 hours to complete. A round trip can take over 14 hours so if possible from experience I would recommend having someone drop you off at one end and pick you up at the other end for ease.