Posts Tagged ‘Superstition Mountains’

The Creation of the Boulder Flatirons

January 18, 2017



Summer Flatirons with Sweet Pea Flowers Captured 29 June 2013 6:45am

We Boulderites love our Flatirons. In the dozen years that I’ve lived in Boulder, Colorado I have taken hundreds of photos of the Boulder Flatirons but I never knew what created these iconic structures. I dusted off my old (unread) copy of The Geology of Boulder County by Raymond Bridge and tried to figure out how the Flatirons were constructed.

Boulder has witnessed a complex geological history including the rise of two Rocky Mountain ranges, the present day Rockies and about 300 million years ago the Ancestral Rockies. Over the past 150 million years, Boulder’s environment ranged from inland seas to floodplains, deserts, swamps, seashores, then back to floodplain conditions again. Each setting deposited layers of sedimentary rock formed by broken fragments of older rock. Out of this rich geological past grew the set of outcroppings which defined the geomorphic term flatiron. There are flatirons all over the world. Other well developed flatirons in the Western US are found in the eastern Uinta Mountains in northwestern Colorado, the Waterpocket Fold in Capitol Reef National Park and the Superstition Mountains near Phoenix, Arizona.



Superstition Mountains Arizona Captured 10 December 2012 @ 5:07pm


The first stage of the construction of the Flatirons was the deposition of a thick layer of sand and gravel which occurred about 300 million years ago when the Ancestral Rockies were completely eroded. Powerful rivers draining these ancestral peaks carried sand and gravel to the adjacent plains, where they accumulated in a massive, 1,000 foot thick sediment that geologists have named the Fountain Formation. The Ancestral Rockies were eventually worn down completely and the eroded material formed younger sedimentary rock layers on top of the buried Fountain Formation. Even our Flatirons are made from recycled materials! 


Frosted Flatirons Captured 27 March 2009 @ Noon

The next stage of the Flatiron’s construction is the result of a unique event that occurred 70-80 million years ago known as the Laramide orogeny. This orogeny caused a renewed period of uplift and deformation from Canada to northern Mexico. The easternmost extent of this mountain building is represented by the Black Hills of South Dakota. This type of event is usually associated with the subduction of one continental tectonic plate under another. The subducted plate melts into a hot layer of viscous molten rock deep under the Earth’s crust known as the asthenosphere. In this instance the subduction zone is off the coast of California where it causes faults like the San Andreas as well as  earthquakes, volcanos, and the Sierra Nevada mountains. This event also uplifted the modern Rocky Mountains and the western great plains.

How could this event have affected Boulder which is 1000km (600 mi) east of the Pacific ocean? Geologists speculate that a particularly low-angled subduction of one tectonic plate beneath the other caused mountainous bulges deep into the North American continent. These forces pushed up the Flatirons and its neighboring mountains. The subducted plate, known as the Farallon Plate took an unusually shallow angle under the North American Plate. The Farallon Plate did not descend into the asthenosphere in the Earth’s mantle until it moved east causing the upheaval of the Colorado Plateau.


Reproduced From Light Train Productions

The sandwich of layers laid down by the erosion of the Ancestral Rockies and subsequent events were uplifted to their present position by this orogeny. Erosion re-exposed the Fountain Formation on the Flatirons.


The third event that made the Boulder Flatirons so unique is the cement that hardened them. Although the Fountain Formation stretches the length of the Front Range, Boulder is unique because of its dozens of well formed flatirons. This is due to a geologic quirk. Here, and only here, the Fountain’s layers are held together by an unusually strong cement called adularia, which is called moonstone when it’s gem-quality. This cement  formed only in Boulder because on two occasions—about 135 million and 94 million years ago warm, potassium enriched water welled up along an ancient fault zone that stretches between Eldorado Springs and Idaho Springs. The Fountain Formation’s grains reacted with that water to form the adularia that tightly cemented its grains together.


Spring Flatirons with Lilacs Captured 26 may 2016 @ 8:30 am

Another consequence of the uplifting of the Fountain formation is that it occurred on the Western Slope of Colorado as well. In the same way a drawbridge is tilted upward to allow ships to pass, the Rocky Mountains rose tilting up the overlying sedimentary rocks. In fact, the other flank of the  “drawbridge” can be seen in Aspen, Colorado on the Western Slope. The iconic Maroon Bells near Aspen form a portion of the Fountain Formation’s western counterpart called the Maroon Formation. Boulder and Aspen are linked by their geological icons.

Maroon Reflections

Maroon Reflections Captured 14 August 2013 @ 7:30am

For those who don’t believe all those geologists and their fancy pants scientific theories and speculations here is an alternative explanation for the construction of the Flatirons. This one was created by Jerry McElroy. He graciously gave me permission for the use of this photo and description of an alternative to the fact-based geological explanation…


Construction of the Flatirons (click to purchase a print)


The construction of the Flatirons in 1931 was the largest building project undertaken by the Civilian Conservation Corps. This massive development was designed to bring jobs to the Town of Boulder, Colorado and to help promote sagging post-depression tourism. Popular tours inside the Third Flatiron were discontinued in 1948 after a Ranger discovered that the interior space was taken over as a convenient den by black bear.


The last time I searched for photos of the Boulder Flatirons there were about 4,350,000 results! Here are some more of mine…


Cold Flatirons Captured 5 February 2014



Smoky Flatirons Captured 7 September 2010 @ 7:37am during Fire Season!



Flatirons from McClintock Trail Captured 13 October 2014 @ 10:50am




Spring Flatirons with Golden Banner Captured 7 May 2007 @ 10:45am




Dawn Flatirons Captured 11 January 2011 @ 7:30am





Mandy the Dog Loved the Flatirons Too. Captured 16 January 2013


I always thought the top of the 3rd Flatiron looks like Mandy the Dog…


The Mandy Flatiron Captured 2 February 2014 @ 1:25pm


This sculpture of the Boulder Flatirons was created by the late Cydd West a local artist who also used recycled materials to form his Flatirons…

Cydd West's Flatirons.jpg

Cydd West’s Flatirons Captured 13 August 2010 at 3:20pm


If you’re in Boulder here’s a nice 3 mi / 4.8 km round trip hike to a big flatiron that I call the Red Slab.



The Red Slab from the East




The Red Slab from the Sky (39°57’51.19N 105°17’7.80W)


To get there take the North Fork of the Shanahan Ridge Trail past the Mesa Trail and you’ll walk right up to this massive flatiron (see the push pin in the above satellite image).



The Red Slab from the Trail



Approach To Slab



The Bottom Of Slab is a Nice Spot to Have Lunch with a Flatiron…



…And Look Up An Ancient Streambed!





Sonoran Sojourn

December 21, 2012

It’s cold and snowy here at the eastern foothills of the Rocky Mountains. Since it’s only a two-day drive from my home in Boulder Colorado to one of the largest and hottest deserts in North America it seemed like a good time to go camping in the desert.

Many of you may recognize the Sonoran desert by its iconic saguaro cactus (Carnegiea gigantea) which is unique to this place. The saguaro is the largest cactus in  the United States, commonly reaching 40 feet (12 m) tall; a few have attained 60 feet (18 m) and one was measured at 78 feet (23.8 m). The cylindrical stems are accordion-pleated; the ridges (outer “ribs”) are lined with clusters  of hard spines along the lower 8 feet (2.4 m) and flexible bristles above this height. White flowers are about 3  inches (8 cm) in diameter; they bloom mainly in May and June and are followed a month later by juicy red fruit. The saguaro’s range is almost completely restricted to southern Arizona and western Sonora. A few plants grow just across the political borders in California and Sinaloa. Saguaro reach their greatest abundance in Arizona Upland. Plants grow from sea level to about 4000 feet (1200 m). In the northern part of their range they are most numerous on warmer south-facing slopes.

Sonoran Saguaro

Sonoran Saguaro

The trip from took me across the Colorado Plateau, an area covering 337,000 km/ 130,000 mi within western Colorado, northwestern New Mexico, southern and eastern Utah, and northern Arizona

I Descended into The Sonoran Desert (33°28'41.53"N 111°14'21.43"W)

I Descended into The Sonoran Desert (33°28’41.53″N 111°14’21.43″W)

My campsite was in Lost Dutchman State Park at the base of the Superstition Mountains

Lost Dutchman State Park Entrance (

Lost Dutchman State Park Entrance (

Named after a fabled lost gold mine, Lost Dutchman State Park is located 40 miles east of the Phoenix AZ Metropolitan Area in the Valley of the Sun. For more than 120 years gold seekers have tried to find a lost mine in these mountains.  Jacob Waltz, known as the Lost Dutchman, died in 1891, at the age of 83. A box of gold was found under his bed after he died. He supposedly described the mine’s location to Julia Thomas, a neighbor who took care of him prior to his death. Neither she nor dozens of other seekers in the years that followed were able to find the “Lost Dutchman’s Mine.” Subsequent searchers have sometimes met with foul play or even death, contributing to the superstition and legend that surround these mountains. Before he died he tried to tell Julia Thomas where the gold mine was located. Jacob left many clues for them to follow, but kept telling them to pay attention because the mine was hard enough to find even if you knew where to look. In 1916, two miners found an old Spanish saddle bag filled with $16,000 worth of smelted gold. This evidence, along with the stories and records of gold transport issued by Waltz, confirms the legend of the Lost Dutchman.

Several trails lead from the park into the Superstition Wilderness and surrounding Tonto National Forest providing the opportunity to find the lost gold if you dare…

Superstition Wilderness

The Superstition Wilderness…There’s Gold in Them Thar Hills!

Here the lack of moisture and extreme heat of summer have evolved a hearty and diverse ecosystem of plants and animals able to tolerate the harsh conditions…



Bird on Saguaro

Bird on Saguaro

Bird in Saguaro

Bird in Saguaro

Jumping Cholla (Cylindropuntia fulgida)

Jumping Cholla (Cylindropuntia fulgida)

Today’s desert gold is water! The Phoenix Metro Area is thirsty for water from Canyon Lake, one of the four lakes created by dams on the Salt River in the Tonto National Forest. The others are Roosevelt Lake, Apache Lake and Saguaro Lake. These dams make life on the Sonoran possible for us humans…

Canyon Lake Brings Water to The Valley of the Sun (( 33°32'31.96N 111°26'11.52W)

Canyon Lake Brings Water to The Valley of the Sun ( 33°32’31.96N 111°26’11.52W)

The geologic centerpiece of the National Forest is Superstition Mountain, formed 25 million years ago by a volcanic crater pushed up over 2000 feet by pressure from below. From my standpoint this resurgent dome was a visual centerpiece and I couldn’t get enough photos. Here’s my favorite taken at dusk. It consists of 4 rows of 22 images merged into a single panorama…

Superstition Sunset Captured 10 December 2102 5:00pm @ 33°28’41.53″N 111°14’21.43″W

My time in the desert was too short but Colorado calls me home despite the cold weather up in the Rockies.

Sonoran Sunset

Sonoran Sunset

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