There is no mountain, nor any thunder, at least while I was there. This art house stands just off on Interstate 80. It was created by an eccentric fellow (aren't they all?) as a memorial to the American Indian who suffered greatly at the hand of the White Man. You can read more about him, his family and his project at thundermountainmonument.
Great photo opportunities to be had. If you are ever in the area, take Exit 145 at Imlay. Fred Lewis is the caretaker there, a real nice guy who unlocked the gate and left me all to myself to wander about. "Just lock up when you leave." Thanks Fred. Hope your prostrate condition gets better.