New regulations for 2012 went in for Cache Creek - no motorized equipment allowed - It used to be possible to high-bank here, but a lot of people were not responsible and left the area in a state of chaos (lots of huge deep holes and trash) and there were some altercations there as well. Its now restricted to panning and river fed sluicing, and nothing else. I suspect if you had a recirculating (electric/battery powered) unit that never entered the creek (you can get buckets of water from the creek), you might be able to use it.
Many places in Colorado are putting restrictions on gas powered pumps in recreational mining rigs - keep that in mind if you are planning on buying anything (High Banker/Dredge) to work in Colorado with. Claims on private land (you need permission to work these) don't have the same restrictions, however, you may still need a permit from the BLM to do anything. They don't want the oil and related polutants in the streams.
Colorado tends to have much more very fine gold than anything else - you don't want the water moving too fast in your sluice, otherwise it will just wash out of it. Fine gold can float on top of the water (surface tension) - this is the stuff that is hard to hang on to, but it does eventually add up if you can capture it.