tnpnt1, if the den was located in a remote area and the adults were not habituated to human presence, they would move the pups quickly after you left. Usually they prepare several dens before whelping and will move the pups to one of them. They have been reported to move the pups as much as two miles away after human intrusion. Usually it is much less. When the pups are a little older and spend much of their time at play outside the den they can quickly trash the area. They accumulate "toys", bones, sticks, trash and little treasures that the parents apparently bring to the den. Last year I found one den that, besides the normal collection of bones and trash, had two nerf footballs that had been badly abused by the pups. Another den located within 1/4 mile of a golfcourse had two stashes of golf balls in "nests" under a mesquite next to the den. There were close to 50 balls in each nest. Most had little teeth marks on them.
Next time you return to the area let us know if you find the new den.