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Idaho’s castles: Inside the towering rock formations just a short drive from Boise


It’s no secret that Idaho is home to breathtaking mountains, stunning lakes and rivers, and miles of wilderness. And as we mentioned in our very first Inside Idaho, it’s coined the Gem State because of its more than 72 different types of precious and semi-precious gemstones found in every corner of the state.

And while there are stunning gems like Idaho’s star garnet buried below Idaho’s dirt… there are remarkable rocks found above the dirt… WAY above. And in this Inside Idaho, we are taking a look at the amazing geological anomaly ascending across Idaho’s countryside found in places like Castle Rock State Park and City of Rocks National Reserve.

The towering rock formations are due to the crustal extension when the earth’s crust is stretched and high-angle faults develop. Mountains uplift and valleys drop, creating distinctive mountain ranges.

“As rocky ranges rise, the newly exposed rock is immediately subjected to weathering and erosion,” according to the National Park Service website. “This rock is attacked by water, ice, wind, and other erosive agents, that have produced many of the geologic features visible today.”

Castle Rock Road

Rock formation of Castle Rock Road. Photo: Anna Daly/BoiseDev.

To get a glimpse at the rocks, sighteers don’t have to travel far. Just a hop, skip and jump away from Boise lies Castle Rock Road, located between Fairfield and Mountain Home off Highway 20. For those heading toward the Sun Valley area in the Wood River Valley – this detour offers some striking scenery along the way.

The winding dirt road takes visitors through towering rock formations with flat faces and stacked boulders – many of them resembling a castle – which is how the area got its name.

While the road is a public thoroughfare, the surrounding land either belongs to the US Forest Service or is private property. It’s a great place to hike around or just drive through. In the spring, you’ll find fields of yellow and purple wildflowers surrounding the rock formations.

Castle Rock State Park

Castle Rock State Park. Photo courtesy: Idaho Parks and Recreation.

In addition to the road near highway 20, it’s important to mention that Idaho is also home to Castle Rock State Park (also located on Castle Rock Road) in Southern Idaho near the Utah state border.

Located in Almo, Idaho in Cassia County, about a three-hour drive from Boise, visitors will find more towering rock formations. The park sits at the base of Cache Peak in the Albion Mountains.

“Evidence suggests that folks have been coming to Castle Rocks for nearly 9,000 years,” the Idaho Dept. of Parks and Rec. website notes. “Campsites are nestled among Idaho’s largest pinyon pine forest on the east slope of the 7,500-foot Smoky Mountain.”

The rugged landscape of the park attracts climbers from around the world. In addition, people go to the park to mountain bike, hike and ride horses. Sightseers will also find pieces of Native American pictographs.

Castle Rock State Park’s visitor center is open from 8 a.m. – 4:30 p.m. Wednesday through Sunday and is closed on Monday and Tuesday. The entrance fee to all of Idaho’s State Parks is $7.00 per car, with additional fees for camping.

City of Rocks National Reserve

Rocky Ridge in the City Of Rocks National Reserve. Photo courtesy:

The park is also just a short drive from the City of Rock National Reserve – a 14,300-acre area of protected land with granite columns tower 600 feet high. The Idaho Department of Parks and Recreation notes that the oldest granite in the reserve is over 2.5 billion years old.

The City of Rocks area got its name when emigrant James F. Wilkens was making his way to California on the California Trail. He described the dramatic geological area as “City of Rocks.” 

Today, visitors can see the same granite spires and monoliths that nearly a quarter-million people who traveled through the area saw between 1843 and 1882.

Anna Daly - BoiseDev Reporter
Anna Daly - BoiseDev Reporter
Anna Daly is a reporter for BoiseDev. She's an Emmy-winning journalist, and a professor at the College of Western Idaho. Contact her at [email protected].

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