Virgin Anticline
The mineral‑rich ridges mined at Silver Reef owe their very existence to the long and complex geologic history of the Virgin Anticline. An anticline, unlike its downward‑curving counterpart, the syncline, is a fold in the Earth’s crust that arches upward. This arching structure is clearly illustrated in the accompanying black and white diagram.
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Anticlines and synclines form when rock layers are pushed, stretched, or compressed by tectonic forces. Anticlines and synclines are common geologic features found all over the world. When a moving landmass encounters a barrier – much like a rug being pushed up against a wall – the layers buckle and fold.
In the case of the Virgin Anticline, the crust between California’s Sierra Nevada and the Hurricane Fault was being pulled apart. The landmass stretching from central Nevada toward Silver Reef acted like the “rug”, moving eastward until it met the Hurricane Fault, which served as the immovable wall. Just short of that fault, the rock layers gave way and folded upward, forming the Virgin Anticline.
When this uplift occurred, the entire sequence of local rock layers – from the striped Moenkopi Formation to the massive Navajo Sandstone that shapes Zion Canyon – was pushed upward together. Over millions of years, erosion removed the upper layers, exposing the upturned strata we see today and leaving the hollow center of the anticline, now occupied by Quail Creek Reservoir.
The following shows layers above anticline before erosion and the anticline’s center behind Quail Creek Reservoir:
Silver Reef Connection
As the anticline rose, the Springdale Sandstone – the layer that hosts Silver Reef’s silver ore – was tilted into long, narrow ridges. These ridges, which roughly parallel today’s I‑15 corridor, were called “reefs” by early settlers because of their sharp, wave‑like appearance. These reefs were barriers to their travel, just like coral reefs in oceans were barriers to boats. See the What is a Reef? article to learn more.
Many of Silver Reef’s mines were driven directly into the sides of these reefs, while others used underground shafts to reach the angled Springdale Sandstone beneath the surface. See the Silver Mining at Silver Reef article to learn more about the importance of Springdale Sandstone.
Without the formation of the Virgin Anticline many millions of years ago, the silver‑bearing sandstone would never have been exposed or accessible. The erosion that shaped the anticline’s modern form occurred gradually over the last 30 million years, revealing the ore-hosting layers that made Silver Reef a viable mining district in the late 1800s.
Interact with the following to reveal Silver Reef’s location in relation to the anticline and its various features by hovering your mouse cursor over each pulsating dot.
Epilog
So, understanding the Virgin Anticline adds another essential piece to the story of how Silver Reef came to be. With a little geological awareness, the evidence of uplift, folding, and erosion is still visible today in the hills and ridges surrounding the historic mining district, a landscape shaped by deep time and revealed by the forces that brought Silver Reef’s mineral wealth to the surface.
What signs of the anticline can you spot in the hills around you today?
Article content by Cliff Bandringa, edited by Kathy Powell
Related Information
- What is a Reef? – Learn how reefs exposed silver ore
- Hurricane Fault – Influenced the creation of the Virgin Anticline
- Triple Junction of Landscapes – Silver Reef sits in the middle