I would say try the national stuff for DEA, BATFE, USSS and search 167-168 for FBI. When I was south of the area near Lytle Creek I heard some encrypted P25. A lot of the agencies in SoCal are moving to P25 VHF and usually encrypted. There's probably near 100 repeaters all throughout San Diego, Orange, LA, etc that I know of.
I don't know what it is you are interested in as far as federal agencies as your question is a bit like asking if there are any good State of California frequencies to listen to in the area. The high desert is a great place to monitor federal natural resource agencies. You will be able to listen to the San Bernardino National Forest (NF), the Angeles NF, and might be able to pick up Frazier Peak on the Los Padres NF depending on your location and antenna. Also listen to the Bureau of Land Management, California Desert District. You should also be able to hear Joshua Tree National Park and Mojave National Preserve. These should all be listed in the database. Also take a look at the Wiki site under common federal frequencies. There you will find the "National Incident Radio Support Cache" frequencies that are used when a large incident (usually a wildfire) breaks. The air to ground and air to air frequencies can be especially interesting.
You should also be able to hear the trunked system over at Edwards Air Force Base. Whenever I travel through that area on my way to Arizona I'm amazed at the distances I can hear things from. The terrain allows for this with a large flat plain, surrounded by mountain ranges, reminiscent of my years in New Mexico, where there is a very high plain, bisected by the Rio Grande Valley, and "island in the sky" mountain ranges, most of which had an electronic site located on them.
This might be a good fire season in the desert and listening to the federal natural resource management agencies in that area might get interesting. A general rule of thumb is that a rainy winter will bring low elevation fires and the mountains will not see nearly as many large fires. With shorter winters, warmer temperatures, and higher fuel loading than ever before, I'm not so sure I would bet on that rule.