Finished up the route trying to figure out belay. Wanted to finish quick as the heat was getting to us. Wasn't much so used cracks around a massive boulder right at the top out. Inspected and seemed solid; didn't budge when I shoved it. Second followed up, stepped directly on top of the said boulder to get safe. The whole thing rocks several centimeters side to side. Both got safe ASAP away from the boulder.