@Kyleboldy2003 asked me a few questions via PM, I hope it's okay i'll share here-hope that's okay.
First thing I didn't understand is that Collecting CA Junipers is generally a totally different thing compared with collecting Sierra Junipers. One of the biggest reasons for this is the environment in which they grow, mainly the fact that CA junipers grow in the dirt and Sierra grow on granite. Both are exposed to the harsh environment which give them all those beautiful characteristics we want for Bonsai. Sierra Junipers are often naturally dwarfed because their root systems are confined to small pockets of soil. Their roots often cannot extend further into the soil because the granite rock is confining them. This is fantastic for Bonsai, because under certain situations you can remove/collect a tree with a nice root system already. The majority of Sierra's that grow in Granite should not be collected as the roots dive deep into granite cracks and would die upon collecting.
With California Junipers they are removed from dirt, sand, clay, etc. They don't grow on rock and extracting them requires a completely different tool and skill set to extract them successfully. I have collected CA and Utah Juniper from dirt with some success, however i'm not an expert in that area and I've decided to focus only on collecting trees from rock where I know my success rate will be very high. I believe that in general the survival success rate for CA junipers is not very pretty, because it's much more challenging to collect a substantial system of fine roots. I know of a few people who have very high success rates with them, but I also know of many people who have low success rate. Often people getting into collecting don't consider aftercare as much as they should. It's important to have a plan for every little aspect of a trees care after you collect it.
This advice only applies to, "pocket trees" with a nice root system after being collected. I think the single best aftercare resource you could get your hands on currently is the Mirai Live video where Randy Knight breaks down exactly what he does. I recommend sifted pumice, a nice tight box, being able to move your trees to different micro climates within your yard, learning to get the correct balance of water and oxygen, leaving the majority of an intact root ball with the original field soil and leaving your newly collected trees on the ground.
To find good locations, start with searching online. There are a million ways to do it, but then at a certain point you'll have to find some roads and start driving/exploring. Then you'll have to find out who owns or manages the land. I've put in a lot of miles, sometimes I'll drive for a few days and not find any good spots. Def stay away from National parks, always ask permission. I've found that asking Permission is an art in itself. Always be extremely friendly, try and build some rapport, and explain that you will leave no trace minus the specimens you want to collect. If you can ask in person that's always better. Maybe find somewhere where you can get permits, then offer to trade locations with a collector who has permits in another location. With the mountains, first you'll spot big old ones growing on rock, you want to find trees with crazy deadwood, twist, curve, ibo jin, etc. then you'll want to look for the little old ones around those big old ones
For collecting in the Mountains, I use a large pry/wrecking bar, a steel frame pack to tie trees to for the hike down, a sharp folding hand saw, full sized Loppers, trash bags and electrical or packing tape. I use to bring a lot more, but that's what I use 95% of the time. It's great if you can find good trees close to your vehicle, but putting in the miles will get you the best trees. I've also drove many gnarly back roads via 4x4 to find good trees. If you want to really get after it, I recommend being in good shape, at least that way you'll enjoy your experience more and you can cover more miles. When I started collecting I weighed 215 and would struggle to run a few miles. I'm down to 185 now, quit drinking so much, eat healthier and got into trail running. It wasn't all motivated by getting better at collecting, but it's much easier for me to put in the miles while collecting now and I have a lot more fun when out collecting. I like the idea of getting in shape to be a good collector, might be a little silly of an idea, but it is some of my motivation to get in shape. Hope this helps, thank you for asking