Determining if an area is withdrawn from mineral entry is part of doing your "Due Diligence". You can determine if it's open to claiming by checking the Master Title Plat maps which are available from the county or many on-line sources.
BLM is well known for dragging their feet, accepting money for a claim that never should have been filed and then not giving a refund. This is one reason (if you're looking to claim) that it is so important to make sure that the area(s) you're interested in are open to entry early in your research. I'm of the mindset that if it's not open to entry, I don't want to bother with it since I'm NOT a recreational miner. If I can't file a claim on it, why should I go to all the effort required to do the rest of the research and testing?
Keep in mind that just because an area is closed to mineral entry doesn't mean that you can't go and dig in it. Many of them you can dig in if you wish to but you just can't file a valid claim for that area. That being said, it's also a very good idea to check the actual withdrawal order. Many areas are withdrawn for a specified period of time. Once that time has expired it will either be re-opened to entry or the withdrawal extended. If you find a good area and the withdrawal period is nearing its end, you an be ready to grab it up if the order is not extended. Like they say... "Fortune favors the prepared Miner".