This boulder tumbled down onto the northbound lane of U.S. Highway 550 on Red Mountain Pass on Monday night. Ridgway resident Neal Mathews was traveling back to Ouray from Silverton, and took this photo just before 6 p.m. after he pulled over and parked his motorcycle in front of the rock. Mathews said it tumbled down just north of the “Ruby Wall” section of the mountain, and he could see the cavity left behind when the rock fell, about 20 feet above the highway. Mathews estimated the boulder was about 9 feet tall. During the springtime, temperature fluctuations can cause freezing and thawing of moisture in crevasses and result in rocks dislodging and falling onto the highway and down the mountain. Some locals call these “pop rocks” for their tendency to “pop” off the side of the cliff and come down. Photo courtesy Neal Mathews