You can enjoy some typically free camping a short drive from Fresno near the Williams Reservoir. The camping area is in Adin California. The camping area is on US Forest Service public land. The camping area is quite primitive. The road to the camping ground is gravel. You can typically stay about 14 days in the camping areas near the Williams Reservoir. The area is on the Modoc NF map so you can download that map is you want a map to take with you as you go hiking while you are camping. In addition to hiking to get some exercise you can also go for walks around the camping area to get some more exercise. There is some amazing wildlife viewing in this camping area. The area also is very under used so typically you can be the only person camping there. At least you may not see any other people the entire time you are there camping which is an amazing feeling. You may even feel like you are in one of the reality show wilderness episodes. The camping is not a set up camp site with multiple cleared areas all next to each other. The camping is actually dispersed camping. The dispersed camping allows you to be out camping and not be interrupted by other people very often if ever. The dispersed camping is inside the limits of the National Forest so all the typical rules such as pack out what you pack in apply as you area camping here. The camping area is near the Hayden Hill Silva Flate State Game Refuge. The dispersed camping area is just off of 139. There are acres and acres and acres of hiking in the camping area. One thing to remember is that there is little to no drinking water in the area so bring supplies to sanitize and filter water or bring in your own water.
The one drawback is that there are no stores or other areas nearby to purchase anything if you forget anything. You can go over 20 km without seeing any stores or other places to buy anything including gas. Please make sure that you bring sufficient gas for your trip to avoid having a very negative experience.