I know by a BLM web page for Idaho, we are allowed to ROCK HOUND for personal Specimens with the use of hand tools and metal detectors and these activities require no permit, fee, or notice provided a number of things you can read for yourself in the BLM Link below. Now in the world of Miners, I have heard the term "Specimen" used to describe any rock they found containing Gold so it was not a nugget, picker, flake, and so on indicating to me, a distinct difference.
This Rock Hounding in Idaho seems to be considered by BLM, a "casual use activity." Now what I have found in other BLM pages for other States is, we are free to do "Casual Prospecting" on lands open to mineral entry. "Casual" from one BLM page of one State to another always seems to imply the same as the Idaho Rock Hounding. It is very low impact, minor to no disturbance, no machinery. I have no idea why BLM as a whole, can not arrive at one interpretation for all States but I do find it varies in some part, the Idaho most obvious. It is my opinion only, that Rock Hounding and Casual Prospecting are one in the same with BLM. Neither however, exempt any responsibility of researching and knowing about what may restrict or prohibit the activity. For instance, Casual Prospecting on a mine claim other than your own, doing this on a mineral lease other than your own. Casual Prospecting on lands withdrawn from mineral entry of which we now have here along parts of the Salmon River, 1/4 mile out each side that has now made it off limits to me and other locals who enjoyed looking for gold but very little was found. As best I can determine, BLM has authority over Mining on BLM and USFS lands though the USFS gets in on the act but the minerals under the water of the Salmon River for instance are under the control of the Idaho Department of Lands but they allow the Idaho Dept. of Water Resources to issue the Recreation Dredge Permit which is seasonal and only certain streams or rivers are allowed to be Recreation Dredged.
I guess what I'm trying to convey is, the guys who sell metal detectors, gold pans, sluices, and dredges, seldom if ever, clue the buyer in on the other stuff that goes with the Hobby. Even myself back in the 1960' and 1970's, thought Ghost Towns and all the Wild West was up for grabs by anyone who owned a Metal Detector or Gold Pan. It's really not so. I know of a whole Ghost town in Idaho that is privately owned.
Now I will tell you, I have never been bothered by the BLM or USFS ever in the field, at least yet. It has been my understanding, BLM tends to be much more than the US Forest Service, geared towards our lands they administer are the Peoples Lands. The USFS has it in their minds that our USFS lands belong solely to them. I found that out personally when face to face in an office, I inquired about Gold Panning and Metal Detecting. I was not frustrated with the girl at the counter who was honestly trying to find and give me the answers. It was the over educated government idiot on the other end of the phone I would have dragged through it and whipped if I could have. In short, everything was pretty much NO , need a notice of intent, unless I wanted to fill out a 9 page form to get a permit to Prospect/Mine. A gold Pan and a Metal detector and you would have thought by the USFS I was going to take a D-10 Cat and dig a hole. No, I have no love for the Federals but I can sympathise when they find 6 foot deep holes left behind or tree roots have been severely undercut and exposed killing the tree. I even saw where a guy was digging to bed rock exposing the bottoms of metal fence post left hanging in the air by the wires.
Anyhow, below is the BLM page for Idaho. I hope it helps but there is more to the research than this and I still have not found cast in stone answers. Just be careful so you don't end up in a Federal Court like a guy here I sort of know did. A BLM Ranger accused him of picking and and keeping a lead bullet from the Indian Wars. Out Metal detecting a river beach here, he found and pocketed it. He was lucky because the Regional head BLM Archaeologist saw it and had the Judge toss the case. It was no more an Indian War artifact than the man in the moon but it cost the guy more grey hairs as if Vietnam was not enough and the time and money to make the long trip.
http://www.blm.gov/pgdata/etc/medialib/blm/id/publications/rockhounding.Par.41703.File.dat/rockhounding_final.pdf