Bubble Rock is a glacial erratic, a boulder the size of a minivan perched on the edge of South Bubble as if one push would send it over. It is Lucerne granite, a rock that formed about 30 miles to the northwest and looks nothing like the Cadillac granite beneath it. The ice sheet carried it here and set it down as the glaciers retreated about 15,000 years ago. Even the Park Service can't agree on its weight. The roadside sign works out to 14 tons, and its website says 100. The boulder is visible from the pull-out on the Park Loop Road, where a wayside tells its story, and from the Bubbles parking area a steep trail climbs South Bubble for a closer look. Bring a camera, and leave the pushing to the photos.
Right there, on the edge of South Bubble. That boulder sitting on the rim, looking as if a good push would send it down, is Bubble Rock. It's Lucerne granite, a different rock from everything around it, and it formed more than thirty miles to the northwest. The ice carried it here and set it down. The Park Service disagrees with itself about what it weighs. Its sign down here works out to fourteen tons and its website says a hundred, so judge it by eye. It has been sitting on that edge since the ice left.
Photo: Christian Collins, CC BY-SA 2.0 · CC BY-SA 2.0