Zion National Park is located along the edge of a region known as the Colorado Plateau. The rock layers have been uplifted, tilted, and eroded, forming a feature called the Grand Staircase, a series of colorful cliffs stretching between Bryce Canyon and the Grand Canyon. The bottom layer of rock at Bryce Canyon is the top layer at Zion, and the bottom layer at Zion is the top layer at the Grand Canyon.
The Utah Geologic Survey produced this free interactive geologic map of the state. Zoom in to identify rock types and ages, as well as volcanic eruptions.
Zion was a relatively flat basin near sea level 240 million years ago. As sands, gravels, and muds eroded from surrounding mountains, streams carried these materials into the basin and deposited them in layers. The sheer weight of these accumulated layers caused the basin to sink, so that the top surface always remained near sea level. As the land rose and fell and as the climate changed, the depositional environment fluctuated from shallow seas to coastal plains to a desert of massive windblown sand. This process of sedimentation continued until over 10,000 feet of material accumulated.
Mineral-laden waters slowly filtered through the compacted sediments. Iron oxide, calcium carbonate, and silica acted as cementing agents, and with pressure from overlying layers over long periods of time, transformed the deposits into stone. Ancient seabeds became limestone; mud and clay became mudstones and shale; and desert sand became sandstone. Each layer originated from a distinct source and so differs in thickness, mineral content, color, and eroded appearance.
In an area from Zion to the Rocky Mountains, forces deep within the earth started to push the surface up. This was not chaotic uplift, but very slow vertical hoisting of huge blocks of the crust. Zion’s elevation rose from near sea level to as high as 10,000 feet above sea level.
Uplift is still occurring. In 1992 a magnitude 5.8 earthquake caused a landslide visible just outside the south entrance of the park in Springdale.
This uplift gave the streams greater cutting force in their descent to the sea. Zion’s location on the western edge of this uplift caused the streams to tumble off the plateau, flowing rapidly down a steep gradient. A fast-moving stream carries more sediment and larger boulders than a slow-moving river. These streams began eroding and cutting into the rock layers, forming deep and narrow canyons. Since the uplift began, the North Fork of the Virgin River has carried away several thousand feet of rock that once lay above the highest layers visible today.
The Virgin River is still excavating. Upstream from the Temple of Sinawava the river cuts through Navajo Sandstone, creating a slot canyon. At the Temple, the river has reached the softer Kayenta Formation below. Water erodes the shale, undermining the overlaying sandstone and causing it to collapse, widening the canyon.
Volcanoes of Zion
Zion National Park sits at the boundary between the Basin and Range geologic province and the Colorado Plateau. This transition zone is part of a volcanic arc from near Delta, Utah, south through Cedar Breaks, St. George, Zion National Park, Parashant National Monument on the Arizona Strip, to the volcanoes of the Flagstaff, Arizona area, and east to Albuquerque north to Capulin Volcano National Monument and even up into southern Colorado. There have been several eruptions in the last million years. The Kolob Volcano (near Lava Point) is the oldest inside the park at 1.1 million years old. Four others erupted along the Kolob Terrace Road 220,000 to 310,000 years ago, including Firepit and Spendlove Knolls. The most recent eruption, known as Crater Hill, erupted just below the West Temple along the Virgin River about 120,000 years ago. However, eruptions in St. George were as recent as 41,000 and 32,000 years ago. The most recent eruptions in the region were near Cedar Breaks about 1,000 years ago, in Parashant 950 years ago, and Sunset Crater 920 years ago. The most recent eruption in Utah was Ice Spring, near Fillmore only 660 years ago. This multi-state volcanic story is explained on the Grand Canyon-Parashant National Monument website in much further detail. The next volcanic eruption in or near the park could happen any time, but also may not happen for tens of thousands of years.
Geology-in-Action A landslide once dammed the Virgin River forming a lake. Sediments settled out of the quiet waters, covering the lake bottom. When the river breached the dam and the lake drained, it left behind a flat-bottomed valley. This change in the character of the canyon can be seen from the scenic drive south of the Zion Lodge near the Sentinel Slide. This slide was active again in 1995, damaging the road.
Flash floods occur when sudden thunderstorms dump water on exposed rock. With little soil to absorb the rain, water runs downhill, gathering volume as it goes. These floods often occur without warning and can increase water flow by over 100 times. In 1998 a flash flood increased the volume of the Virgin River from 200 cubic feet per second to 4,500 cubic feet per second, again damaging the scenic drive at the Sentinel Slide.