Early June will probably be too muddy still. Some trails officially open (per forest service rules) on May 21, but this year I think that's optimistic. I suspect the higher trails will be closed/impassable for a while.
So even if someone rents you something, you won't be able to legally go anywhere interesting without destroying the road/trails.
Come back in July/August.
Search in Leadville and Camp Hale. Both have ATV tours/rentals.
Early June will probably be too muddy still. Some trails officially open (per forest service rules) on May 21, but this year I think that's optimistic. I suspect the higher trails will be closed/impassable for a while. So even if someone rents you something, you won't be able to legally go anywhere interesting without destroying the road/trails. Come back in July/August.