Tony
It is illegal to remove artifacts anywhere due to the antiquities act.
It is illegal to remove anything from national parks
It is ok to remove a limited amount of minerals, like agate, petrified wood and invertebrate and plant fossils from non-park federal lands such as BLM.
You can not remove vertebrate fossils or dinosaur bones, and you can't make castings of dinosaur foot prints.
A lot of habitation sites have been looted over the year however

Peter