This is the den where this years pups were born. They stayed here until the first of May, then moved them to another den. They may do this several times a season probably for safety reasons. Often, they make their dens near human dwellings to dissuade coyotes. After inspecting this empty den, I discovered they had taken up residence near a seldom used camp, where they had denned in years past.
There are always two or more ways to get in or out.
On top of the den I noticed they had left a scrap of prey fur (woodchuck? ) that I had watched the pups play with often. When I picked it up, it reeked of fox! A scent marker now.