Please note that for 2014 all riders in the A and B events (CX1/2 Men, CX3 Men, and CX1/2/3 Women) must have a cyclocross style bike (tires max 34 mm wide, road style handlebars NOT straight bars, max width of bars 50 cm). This requirement is still more liberal than the UCI standard.
In 2009 and 2010 the cyclocross committee published rules outlining that all categories except the lowest would require a cyclo-cross bike. A lot of time has been given for riders to adapt to the equipment rules. Riders in the C event (CX4 men, CX4 women, and citizen racers) will still be allowed to use mountain bikes that conform to UCI MTB standards (i.e. no bar ends, no studded tires, at least two functioning brakes, no aero bars, etc.)
Note that to participate in Nationals all bikes will have to conform to UCI standards, the most obvious difference with ours being a max tire width of 33mm.