Picket Wire Canyonlands is a remote canyon of the Purgatoire River on the Comanche National Grassland south of La Junta, and it hides one of the most remarkable sights in Colorado: the largest dinosaur tracksite in North America. More than 1,900 footprints in about 130 trackways run across the riverbank rock, joined by rock art, a pioneer mission and a historic ranch along the way.

About 150 million years ago this area was the muddy shore of a large lake, and dinosaurs left their footprints as they walked along it. Long-necked Apatosaurus (better known as Brontosaurus) moved through in groups, and meat-eating Allosaurus left three-toed tracks nearby. The mud hardened into rock, and the Purgatoire River eventually carved the canyon that exposed the trackways. People have lived here for thousands of years too. Rock art on the canyon walls is estimated to be between 375 and 4,500 years old. In the late 1800s Hispanic settlers farmed the canyon bottom, and the ruins of the Dolores Mission and its cemetery, built around 1898, still stand. Farther downstream, the Rourke Ranch, founded in 1871, grew into one of the area’s big cattle operations and is now on the National Register of Historic Places.

Getting to the tracks takes some effort, which is part of the fun. Hikers, mountain bikers and horseback riders start at the Withers Canyon Trailhead and drop about 250 feet into the canyon, then follow an old ranch road along the river past the mission ruins to the tracksite, 11.2 miles round trip. Continuing on to Rourke Ranch makes for a roughly 17-mile round trip. The only motorized access is the Forest Service’s guided auto tour, offered on selected spring and fall Saturdays, when visitors drive their own high-clearance four-wheel-drive vehicles behind a guide and stop at the tracks, the mission and the ranch. However you get there, standing beside a line of Brontosaurus footprints by the river is something you won’t forget.

The fall 2026 guided auto tour season is wrapping up, and spring 2027 tours are expected to go on sale on Recreation.gov in early March, so watch for them if you’d rather drive than hike. The trail stays open year-round for day use, and cool late fall days are a good time to make the long hike to the tracks. Check the Forest Service page for alerts before you go.