Mast Park (From the Santee Walmart) From 52, exit Mission Gorge Rd. heading East, turn left on Town Center Parkway. From 67, I cant figure it out from the map, what a mess. Find yourself on Mission Gorge Rd heading West, turn right on Town Center Parkway. Turn Left into the Walmart Parking Lot and park in the North West part of the parking lot. A trail heads out of this corner and heads North. Stream, bridge, trees.