Inverted topography is a geomorphologic feature that
describes topographic high points that were once ancient
valleys. To form this example of inverted topography, lava
initially filled an ancient canyon where it cooled and formed
a hard weather resistant basalt. The surrounding sandstone
eroded away more quickly leaving the basalt higher than the
surrounding area. Thus the former canyon turned into the
ridge, inverted topography.
About 1.41 million years ago, the Lava Ridge flow filled the
ancient Snow Canyon that ran to the east of the coordinates behind
what is now the Winchester Hills subdivision. 
The more resistant basalt displaced the Snow
Canyon drainage to the west where it eroded down a new channel
leaving the Lava Ridge flow at a higher elevation.
Image Source: Utah Geological
Survey(http://geology.utah.gov/surveynotes/geosights/invertedtopo.htm)
About 1.16 million years ago, the Snow Canyon Overlook flow
filled the displaced drainage. Again, the Snow Canyon drainage was
displaced to the west, eroding the current Snow Canyon out of the
more easily eroded sandstone, leaving the Snow Canyon Overlook flow
in the vicinity of the coordinates provided.
Then between 10,000 and 20,000 years ago, the
Santa Clara flow filled the current Snow Canyon. Much of the
floor of the current Snow Canyon is filled with the basalt of
the Santa Clara flow. Some of the high ridges of sandstone
remained above the lava flow like islands and form “turtle
backs.” As before, the drainage is being forced off to the
side of the basalt at Hackberry Wash (If someone could get
coordinates for this it would be greatly appreciated. I was
unable to find it).
Image Source: adapted from Higgins, 2003
Additionally, the end of the Santa Clara flow is slowly being
eroded back up the canyon creating an approximate 40 foot cliff.
This can be accessed along Johnson Trail. (The trail is closed from
March 15 to October 31 for nesting. When it opens, can someone
please send me coordinates for this location).
The result of this geologic process is that the oldest basalt
flow sits at the highest elevation, while the youngest lava flow is
found at the lowest elevation.
Additional examples of inverted topography can be found
throughout St. George, such as the bluff that the St. George
Municipal Airport is built on and the basalt capped ridge that I-15
runs through.
Logging requirements:
Send me a note with :
- The text "GCZ9C6 Inverted Topography – Snow Canyon" on the
first line
- The number of people in your group.
- the number of "turtle backs" you can see in each of the three
different flows.
The above information was compiled from the
following sources:
- Higgins, Janice M. Geology of
Snow Canyon State Park, Utah in Geology of Utah’s Parks and
Monuments, 2003 Utah Geological Association Publication 28 (second
edition) D.A. Sprinkel, T.C. Chidsey, Jr. and P.B. Anderson,
editors
- Utah Geological Survey, Inverted Topography in
the St. George Area of Washington County,
http://geology.utah.gov/surveynotes/geosights/invertedtopo.htm
- Foos, Annabelle and Bruce Simson, Geology of
Zion National Park, Coral Pink Sand Duens State Park and Snow
Canyon State Park,
http://www2.nature.nps.gov/geology/education/foos/zion.pdf