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Hike We Like: The Cretaceous-Tertiary Loop

Hike the eastern edge of Golden's South Table Mountain, the land where dinosaurs once roamed—and died.

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Why we love it: Stunning views of downtown Denver from South Table Mountain’s precipitous eastern edge, with some fascinating geology along the way.

When to go: An hour before sunrise, to watch dawn’s first light shine on the city—and the Front Range.

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The nearly 2.5-mile-long Cretaceous-Tertiary boundary explores the southeastern corner of Jefferson County’s South Table Mountain Park. Two trailheads access this area, offering a total of four miles of trails open to hikers, mountain bikers, and horseback riders.

From the trailhead on Denver West Parkway, I recommend following this loop clockwise, hiking first up the well-graded Cretaceous Trail. After one mile, this smooth, easy-to-follow path joins up with the Basalt Cap Loop, whose level gradient offers a pleasant respite along the mesa’s flat top. For the best views, continue left at the first junction with the Basalt Cap Loop to follow its northern side, which leads to a fantastic overlook at the northeastern-most point.

From the overlook, downtown Denver’s glassy skyscrapers seem to rise just beyond the mesa’s edge. Boulders of dark basalt, part of the cap for which the trail is named, create a dramatic foreground. This basalt is the remnant of a lava flow that erupted 64 million years ago from a Front Range volcano located northwest of here. It erupted just 1.5 million years after one of the worst extinctions in our planet’s history, which marks the division between the Cretaceous (abbreviated as ‘K’) from the Tertiary (‘T’) periods. Geologists have determined that the extinction was caused by an enormous asteroid, which smashed into Earth 65.5 million years ago, kicking up enough dust to blot out the sun, igniting a global firestorm, creating acid rain, and ultimately killing half of the species then alive, including the dinosaurs.

This side of South Table Mountain is the first place in North America where the K-T boundary was identified, not far from where the Tertiary trail branches off from the Basalt Cap Loop. So as you descend the Tertiary Trail to return to your car, your feet will cross the infamous K-T boundary, the time when the dinosaurs died.


Getting there: From Denver head west on I-70 to Exit 262 (Colfax Avenue). Merge onto West Colfax toward US 6. Turn right on Moss Street, then turn right again onto South Golden Road. Take the first left onto Kilmer Street and follow this to its end in 0.2 miles at Pleasant View Community Park. Park here and follow the dirt loop counter-clockwise until a separate dirt path branches off, heading toward South Table Mountain. Follow this path, and then use the crosswalk in front of the large NREL entrance sign to access the beginning of the trail.

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Tips: Dogs are allowed but must be on leash. South Table Mountain Park protects a number of sensitive areas; please respect all signed closures.

(Check out more hikes we like)

Terri Cook, 5280 Contributor

Terri Cook is an award-winning freelance writer based in Boulder. More of her work can be found at down2earthscience.com.

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