Haha! Steriods are the last thing any squirrel needs.

I think your marmot is what we call a groundhog. (At first I thought you meant those golden monkeys in the rainforest! That might be a marmoset, though...)
I've seen some of those in the pastures around here, But they're much too big and fat to be what I saw. The ones around I've seen tend to lumber around, too. This thing moved more like a beetle; its legs moved, but it's body didn't.

This has got to be the weirdest thing I've ever tried to describe. But you're right--I'm having fun trying to figure it out. I'm trying to think of things to compare it to, but nothing really matches. It was almost like a small possum or large rat, but without a tail, with different legs, and less of a neck.

There weren't any ponds or streams nearby (as I was in a development), but it may have been a muskrat who lost its tail to a snapper. I'm looking at a list of PA mammals right now.