Mud Volcano is a loop of boardwalk and pavement on the left for northbound drivers, 0.6 mile, with two steeper pitches. The National Park Service allows one to two hours, and the lower loop, which begins on the lot's northeast side, is accessible. Vault toilets are at the lot. The area changes on a scale people can watch: one named feature destroyed itself in 1872, another did not exist before 1948, and part of the hillside has been cooked by rising heat. The most popular feature is Dragon's Mouth Spring, whose growl carries to the boardwalk. Sulphur Caldron, a strongly acidic spring, has its own small roadside pullout just to the north.
Your nose may find it first. The Mud Volcano lot is on your left in about a third of a mile. Watch for oncoming traffic before you cross. The loop is six-tenths of a mile of boardwalk and pavement with a couple of steep sections, and the park allows one to two hours. The lower loop is accessible, starting at the northeast end of the lot, and there are vault toilets. Nothing here holds still. Mud Volcano itself is just a pool, because it blew away its own top in eighteen seventy-two. Black Dragon's Caldron didn't exist before nineteen forty-eight, when it exploded into being, knocking trees down and showering the forest with mud. Dragon's Mouth Spring boils out of a deep cave, where pressure bubbles burst against the roof, and the booming carries out to the boardwalk like an animal growling. The ground shakes here. A seven-month earthquake swarm in nineteen seventy-eight was followed by more heat and dying vegetation on a slope called Cooking Hillside. Tree rings show gas discharge more than doubled, and the researchers concluded the gas pressure itself may have caused the swarm. So this hillside may have been shaking itself. Turn left out of the lot to keep heading north. Just past the lot, on your right, Sulphur Caldron has a small pullout. Its water has a pH of about one to two, close to battery acid.
Photo: NPS Photo / Matt Poyner · Public domain