Toadstools, UT 2012
In May of 2012, I took a small group of students and Faculty friends to the Utah and Arizona border to witness the Annular Solar Eclipse. While there, we explored the Wahweap and Rimrocks (Paria) Toadstools.
These unusual rock formations began forming over 100 million years ago in the Utah area. A “hoodoo” is a column of weathered rock, formed when a thick layer of soft rock is covered by a thin layer of hard rock.
Sometimes, when cracks in the hard rock allow the underlying soft rock to erode, one small cap of the hard rock is resistant to cracking, and it protects the underlying soft rock. This cone of protected rock eventually takes the shape of a vertical pinnacle.
These white sandstone spires, which have been named everything from “goblins” to “white ghosts,” look like they came straight out of the mind of Dr. Seuss.
The 9.2 mile trail begins at the confluence of Coyote Creek, Wahweap Creek, and the peculiarly-named Nipple Creek, where you will hike under direct sunlight on the Wahweap Wash. At the 0.5 Mile Mark you will reach the dilapidated “Hanging Fence”, and finally, by the 3.6 Mile Mark, you will have entered the first of the Wahweap Toadstools (Hoodoos).
These fotogenic Toadstool/Mushroom-like features were created by 2 types of rocks with contrasting erosional characteristics.
The pedestal part of the toadstools is white sandstone and believed to be the Gunsight Butte Member of the Entrada Sandstone Formation.
Pictured below, the Gunsight Member is the white fine-grained massive sandstone with a red layer at the bottom forming most of the high cliffs in the Rimrocks, (seen later).
Pictured below, the Wahweap Creek Toadstools have a reddish conglomerate capstone or topknots. On the canyon wall this is the layer immediately above the white Gunsight Butte Member.
The Gunsight Butte is a white fine-grained friable, (which means the grains of sand can be rubbed off easily) sandstone.
The unique thing about the Gunsight Butte Member is, when it rains and the outer surface of the pedestal gets wet, gravity pulls the outer centimeter or so down and it looks just like flowstone on most limestone caves. It’s as if these pedestals are made of sugar and with each rainstorm are slowly melting away.
This is truly a unique place. The Gunsight Butte Member in this area, appears to fall into the category of Quartz arenite, (more than 90% of the grains are derived from quartzite). The cement or matrix holding the grains together is calcium carbonated, a kind of limestone.
Over thousands of years, parts of the limy sandstone or conglomerate caprock broke off and rolled downhill to rest on top of a bench or a more eroded part of the Gunsight Butte Member.
Then the caprock, being more weather-resistant, shielded the softer white fine-grained sandstone below from eroding away.
After many years, all that’s left is a pedestal and a chunk of capstone balanced on top or fallen nearby.
Pictured above, the capstone in “The Rimrocks” is a gray more weather-resistant sandstone with some limestone, (at least the erosional features look like limy sandstone).
The Rimrocks could be from an upper layer of the Entrada, Henrieville or Dakota Formations. For sure, it’s from one of the layers above the Gunsight Butte, and below the Tropic Shale.
Just east of the Wahweap mushrooms and north of US 89, is the red Paria Rimrock Toadstools. These toadstools are formed identically as the Wahweap toadstools, but within a lower-older layer of the Entrada Formation. This red standstone pedestal is immediately below the Gunsight Butte Member. But the capstones are of the same resistant rock.
The Paria Rimrocks contain cliffs, buttes, hoodoos, and badlands: all carved from sugar-white and cinnamon-red sandstone. The Rimrocks look like a geological confectionery.
From the trailhead next to US 89, a well-worn path follows a sandy wash northward. After about a kilometer, the trail climbs through some badlands, and right to the base of Toadstool Hoodoo. The hoodoo sits on the edge of a broad, red terrace. The trail continues up to the top of this terrace, where more hoodoos stand huddled in a small cluster. They are easily seen from anywhere atop the bench. Tall white-grey cliffs rise to the north.
The Rimrock bench stretches away to the west. The land below Rimrock bench slopes up into a scenic mess of red and white badlands, then falls away abruptly into an adjacent valley. To the east, the Rimrock bench is bordered by a low ridge. The far side of this ridge forms one wall of a white-rock canyon that winds northeast for 2 km before narrowing. In the distance, the surrounding area consists of washes, mud hills, and eroded, multicolored buttes. The Rimrocks stretch for about 3.2 km westward.