The Cottontail Observatory is located on 82 acres of private land about 6 miles SE of the town of Twin Bridges, MT. Twin Bridges is about 30 miles south of interstate 90, Southeast of Butte, and about 26 miles south of Whitehall, exit 249.
This is a DARK site at night. There is just the faintest glow on the Northwest horizon towards Butte. The few lights on the farms in the valley, about 3 miles away, are actually below the horizon from the site (elev. 5,400 ft) and not really an issue. BLM land borders the site to the north and east, and it is also accessible (but you have to go through the site to get to it).
From Twin Bridges, take Hwy 287 towards Sheridan. At 3 miles, turn left on Wet Georgia Road. There is a sign for Cottontail Observatory. You will cross 3 cattle guards. After the third cattle guard, follow the road to the left. Travel 1 mile to the site. Below is a Google map of the area and photos of the site itself.