Hello Rob,
The area you are referring to is Jefferson county open space and BLM wouldn't have any say there.
You can find details about that area from our
"free panning and sluicing areas" thread here in the forum.
You can contact the county to ask for exceptions to their rules but I believe they said no motors, but panning and sluicing is just fine.
Happy prospecting and stay safe out there. Remember everyone, reclaim/refill all holes dug before leaving too.
CP