From 635, exit Oates and head north. (Oates is on the northern edge of Mesquite) 
Go down the hill, past Northwest Highway, then up the hill to the traffic light where O'Bannion crosses Oates. (about the third light, I think) On the left will be a strip shopping center. At the light, turn RIGHT, then take an immediate left... you're now in the Rec Center parking lot. Straight ahead will be the center and gym. Park and haul out your gear!