Go to the management agency for the land, be it USFS, BLM, State, etc. You might also check with the State mineral/environmental office. See what the requirements are for what you're wanting to do.
As to Federal agencies, the trigger point is usually any equipment beyond hand tools. No idea on what the State requirements are. If planning on some kind of wash plant you're probably going to have some kind of settling pond for the fine tailings.
For the feds, an excavator will usually require a Notice Of Intent (NOI) at the minimum, and a Plan Of Operation, (POO) and a reclaimation bond, the amount depending on what disturbance is allowed at one time. Usually required to reclaim a worked area before opening another.
If you are going to have to file a NOI/POO, plan on quite a bit of time to get it approved. I know of some still in process for 5 years and still not issued. The responsible agency can give you a possible time frame, as well as asking the State for their time frame if they're involved.