The wreck on Big Dipper (skiers right where A-Street enters) is a Bombardier Muskeag. It isn't a groomer but a tracked utility vehicle. Loon still has one and it is primary used durning non winter months for trail construction and maintenance. The story I've heard about the Dipper wreck is while was being used during construction of the East Basin trails ( 1968 ) it overheated, caught fire and was destroyed. Allegedly the fire burned off the mulch and grass seed that had been spread over the newly graded trail. Its likely the Muskeag was hauling mulch and/or seed. This incident is one of the "Troubles" that inspired the naming of the trail "Triple Trouble".
If your looking to spot the wreck start with a ride up the East Basin Double, it will be on your left set back into the woods five feet or so.
Thanks for the real scoop!