Boulder's unique rock formations. Photo by Flickr user Christian Collins

Guide to Boulder’s Natural Attractions


From the Pearl Street Mall to the historic Chautauqua Cottages, Boulder’s full of interesting history, old buildings and unique shops.

But with a name like “Boulder,” the true attractions were here long before the settlers raised a hammer. The stars of this region are the foothills and mountains, the curious geological formations and the nature that surrounds us.

Here’s a look at some of Boulder’s coolest natural attractions.

The Flatirons

The Flatirons. Photo by Ann Duncan

Of course, Boulder’s rocky mascot is impossible to miss. You can get up close and hike or climb them or admire them from afar.

The Flatirons are part of a bigger sedimentary rock family called the Fountain Formation, dating back about 280 million years ago with roots in the Ancestral Rocky Mountains. The famous Maroon Bells in Aspen are also part of this formation. So you could say the Flatirons and Maroon Bells — two of Colorado’s most photogenic sites — are siblings.

The flat, nearly vertical shape of the Flatirons actually started as a flat, horizontal layer, but it was tilted as the region uplifted about 65 million years ago. So the distinguishable Flatirons, as we think of them today, are relatively young — for a rock formation.

There are five main Flatiron formations named (simply) the First, Second, Third, Fourth and Fifth Flatirons. Read the Guide to the Flatirons here.

Green Mountain

Green Mountain. Photo by Flickr user Thomson20192

Boulder hikers consider there to be three big summits in the area to conquer: Green Mountain, Bear Peak and South Boulder Peak. Green Mountain, 8,144 feet, is the most accessible to hike. Start in Gregory Canyon, just beyond popular Chautauqua Park. It’s a long, multi-mile hike with some challenges, but nothing too technical, so you can feel like you’ve mastered a real mountain, not just a casual hike.

Green Mountain is part of the Front Range of the Rocky Mountains. Although it’s not one of the “fourteeners,” or mountains 14,000 feet or taller, it is famous for the Flatirons on its eastern side and its proximity to Boulder. Beyond the five major Flatiron formations, there are hundreds of other interesting, smaller rock formations scattered around Green Mountain. Some have funky names, like Satan’s Slab and The Fatiron (that’s not a typo).

Flagstaff Mountain

View from Flagstaff Mountain. Photo by Flickr user Max and Dee Bernt

Flagstaff is Boulder’s mountain. Drive to the top of it for some of the region’s best views, and enjoy a high-end dinner at the Flagstaff House where the scenery from your table is as delicious as the dishes.

Flagstaff Mountain is old, for this area. The igneous rock that comprises this mountain dates way, way back about 1.7 billion years (originally as molten minerals deep inside the planet). The mountain you can drive up today is the result of erosion all the way down to the ancient center.

Royal Arch

Royal Arch. Photo by Flickr user Christian Collins

It’s not as dramatic as the famous rocky arches in Utah, but Boulder’s Royal Arch is still an incredible natural attraction to behold — if you can endure the hike. The Royal Arch Trail is not long, only about 3.5 miles round trip, but there’s significant elevation gain, rocky parts and can be tricky to maneuver. It’s still doable for many hikers, but the challenge tends to surprise people who are expecting a lazy stroll.

The Royal Arch, 6,915 feet above sea level and stretching into a 20-foot upside-down U, is another remnant of the Fountain Formation. Geologists believe the arch was sculpted into its interesting shape by water, wind and erosion.

Mount Sanitas

Hiking Mount Sanitas. Photo by Flickr user Mario Lurig

Mount Sanitas is an inseparable part of Boulder. For many locals (you’ll know how many when you see how busy the trails can get), hiking this small but somewhat aggressive mount is a regular part of life in Boulder. It’s often a go-to hike for visitors who want to “summit” a rock that won’t take all day and is close to downtown. The trail is considered moderate to difficult.

Mount Sanitas trailhead. Photo by Flickr user James Tiffin Jr.

This iconic landmark also has an interesting history. First, it’s home to sandstone quarried for the very first buildings on the University of Colorado campus. Second, it was named after a sanitarium (or health spa) that is now the Mapleton Medical Center. Back in 1895, Seventh Day Adventists founded the sanitarium and hospital; it’s believed the first hikers were tuberculosis patients. The dry climate and altitude were supposed to help improve breathing.

Learn more about Mount Sanitas’ background here: Hiking in Mt. Sanitas.

Eldorado Canyon

Eldorado Canyon. Photo by Flickr user F Delventhal

Eldorado Canyon State Park is known for its incredible rock climbing — more than 1,000 routes. But non-climbers can appreciate the beauty of this region, just as well.

Eldorado Canyon has two areas: the Inner Canyon is more developed, whereas Crescent Meadows is undeveloped. In total, it spans about 885 acres. The canyon is billions of years old.

Human history here dates back to the Ute Native American tribes, who liked the area for its naturally occurring hot springs. Historians believe the Ute lived in the canyon walls, which provided protection from Colorado’s harsh winter conditions. Settlers in search of gold followed. In the early 1900s, it was used as a fancy resort region for wealthy and famous people.

Read more about planning a trip to Eldorado Canyon.

Boulder Reservoir

Boulder Reservoir. Photo by Flickr user SparkFun Electronics

It’s popular for swimming, boating and outdoor activities, but Boulder’s main body of water is not exactly a “natural” attraction. The 700-acre Boulder Reservoir was actually built in the ‘50s. It used to be the spot of a dairy farm. Even the sand for the “beach” was delivered; 75 tons of it.

The lake was built to store irrigation and drinking water, but it turned into a hotspot for all kinds of water fun. Today, it supplies about 20 percent of Boulder’s drinking water and provides homes to various fish and wildlife, from owls to prairie dogs.

Another large body of water near Boulder is Gross Reservoir. Learn more about Gross Reservoir (you can camp there!) here: Boulder’s Hidden Gem Where You Can Camp.

Boulder Creek

Boulder Creek. Photo by Flickr user David Gibbs

Boulder Creek runs right through Boulder, making it a favorite focal point for fly fishing, tubing and hanging out. It flows through Boulder Canyon and past downtown, the library and Central Park.

The creek itself stems from two main tributaries: the North and Middle Boulder Creek, from the Continental Divide. It later merges with South Boulder Creek. Beyond Boulder, the creek keeps flowing into Weld County and eventually joins St. Vrain Creek — and ultimately the huge Mississippi River and the Gulf of Mexico.

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