Sibley Volcanic Regional Park

Sibley Volcanic Regional Park offers a self-guided tour of Round Top Volcano, active 10 million years ago. You can pick up a brochure at the Skyline Boulevard staging area. Examples of the park’s rock formations can be viewd at an outdoor display at the entrance. Here are a couple of views from the park and tour.

Old Quarries opened up cross sections of the bedrock geology

A softer layer of brick red tuff is sandwiched between two layers of hard lava. The lava baked the tuff, causing oxidation which results in the red color. Sibley Volcanic Regional Park, December 29, 2025

This brick-red knob is made of cinder that erupted from Round Top and landed while it was still hot, fusing the volcanic fragments together. Sibley Volcanic Regional Park, December 29, 2025