Geological History of Zion National Park
Zion National Park has been shaped by many geological processes over the years, well, millions of years, and fortunately for us, due to the sparse vegetation and arid climate large expanses of bare rock have been exposed to let us all in on the geological history of the park. Located along the Colorado Plateau, the rock layers of the region have been constantly uplifted, tilted and eroded to form a feature known these days as the Grand Staircase, colorful cliffs which stretch all the way between Bryce Canyon and the Grand Canyon. I bet you thought that there was something familiar about the photos! Anyway, get this . . . the bottom layer of rock which forms Bryce Canyon is the top layer of rock at Zion, and the bottom layer of Zion is the top layer of the Grand Canyon. See, that’s what uplifting and tilting does for you . . . makes things all up and down and topsy turvy!
Geology of Zion National Park
Around 240 million years ago Zion was pretty much a flat basin around sea level, but gravel, sand and mud was constantly eroded from the surrounding mountains and streams carried the materials and deposited them in layers into the basin. As these deposits became heavier, the weight of them made them sink into the basin, so the surface of the basin remained at around sea level. With the rising and falling of the land and climate changes the environment was changed between shallow seas, coastal plains and deserts. This continued until there was around 10,000 feet of stuff accumulated in the area, that’s pretty thick!
Next came the lithification . . . lithifica-what? Water filtering through the sediments, not just any old water either, but water ladened with minerals – iron oxide and calcium carbonate – the layers were cemented by silica and pretty soon all of that weight and pressure compressed the layers into stone. These ancient seabeds were transformed into limestone, the mud and clay deposits were transformed into shale and the desert sands became . . . you’ve guessed it, sandstone. Every layer is unique in its color, thickness and mineral content . . . just a part of the incredible beauty of Zion National Park.
Pretty soon (I keep saying that, but actually we’re talking thousands if not millions of years) – forces within the Earth’s crust started to push upwards, slowly hoisting blocks of the crust vertically until the elevation at Zion rose from sea level to an astonishing 10,000 feet high. This uplift is actually still going on.
What comes after sedimentation, uplift and all those other geological factors . . . yep, erosion. All of that uplift gave more power to the streams, they became more fast moving and were able to cut down on their steep descent towards the sea, fast moving streams can carry more sediment than slow moving rivers, and they began to erode and cut into the rock layers, forming deep, narrow canyons. The Virgin River is still at it to this very day, excavating as it heads on its merry way.
When I said narrow canyons, I meant narrow canyons!