They shoot 1000 yard prone in Wendover. http://www.usrpa.org/High_Power/2011/2011calendar.html
We will also be starting some 1000 yard prone matches in Hotchkiss, Co. this year. First one is in May. There was talk of putting some benches in but I haven't heard anything about that recently.
There is also a new very nice range that just went into Price, UT (south of SLC about 2 hrs.) I don't know that they are actively shooting competitions yet, but their seems to be quite a bit of interest. I haven't seen it, but was told the range is very nice and someone put a lot of money in it. Try the Carbon County website for info.
Good Luck
Edward