Vacations Blog

Although its awesome grandeur and beauty are the major attractions of the Grand Canyon, perhaps its most vital and valuable aspect lies in the time scale of Earth history that is revealed in the exposed rocks of the canyon walls. No other place on Earth compares with the Grand Canyon for its extensive and profound record of geologic events.

The canyon’s record, however, is far from continuous and complete. There are immense time gaps, many millions of years are unaccounted for by gaps in the strata in which either vast quantities of Earth materials were removed by erosion or there was little or no deposition of Earth materials. Thus rock formations of vastly different ages are separated only by a thin, distinct surface that reveals the vast unconformity in time.

Briefly summarized, the geologic history of the canyon strata is as follows. The crystallized, twisted, and contorted unstratified rocks of the inner gorge at the bottom of the canyon are granite and schist about two billion years old. Overlying these very ancient rocks is a layer of limestones, sandstones, and shales that are more than 500 million years old. On top of these are rock strata composed of more limestones, freshwater shales, and cemented sandstones that form much of the canyon’s walls and represent a depositional period stretching over 300 million years. Overlying these canyon rocks is a thick sequence of Mesozoic Era rocks (245 to 66.4 million years old) that form precipitous buttes remnants and the vermilion, white, and pink cliff terraces of southern Utah but which have been entirely eroded away in the area of the Grand Canyon proper. Of relatively recent origin are overlying sheets of black lava and volcanic cones that occur a few miles southeast of the canyon and in the western Grand Canyon proper, some estimated to have been active within the past 1,000 years.

The cutting of the mile-deep Grand Canyon by the Colorado River is an event of relatively recent geologic history that began not more than six million years ago, when the river began following its present course. The Colorado River’s rapid velocity and large volume and the great amounts of mud, sand, and gravel it carries swiftly downstream account for the incredible cutting capacity of the river. Prior to the building of the Glen Canyon Dam, the sediments carried by the Colorado River were measured at an average of 500,000 tons per day. Conditions favorable to vigorous erosion were brought about by the uplift of the region, which steepened the river’s path and allowed deep entrenchment.

The depth of the Grand Canyon is due to the cutting action of the river, but its great width is explained by rain, wind, temperature, and chemical erosion, helped by the rapid wear of soft rocks, all of which steadily widened it. Amazingly, the canyon was cut by a reverse process, for the river remained in place and cut through the rocks as the land moved slowly upward against it. Only thus can be explained the canyon’s east-to-west course across a south-facing slope and the presence of plateaus that stand across the river’s course without having deflected it.

The most significant aspect of the environment that is responsible for the canyon is frequently overlooked or not recognized. Were it not for the arid climate in the surrounding area, there would be no Grand Canyon. Slope wash from rainfall would have removed the canyon walls, the stair step topography would long ago have been excavated, the distinctive sculpturing and the multicolored rock structures could not exist, the Painted Desert would be gone, and the picturesque Monument Valley would have only a few rounded hillocks.

Grand Canyon National Park is one of the world’s premier natural attractions, attracting about five million visitors per year. Overall, 83% were from the United States: California (12.2%), Arizona (8.9%), Texas (4.8%), Florida (3.4%) and New York (3.2%) represented the top domestic visitors. Seventeen percent of visitors were from outside the United States; the most prominently represented nations were the United Kingdom (3.8%), Canada (3.5%), Japan (2.1%), Germany (1.9%) and The Netherlands (1.2%).

This canyon is a gift that transcends what we experience. Its beauty and size humbles us. The Grand Canyon we visit today is a gift from past generations. Take time to enjoy this gift. It is more than a pleasuring ground for those that explore the roads, hike the trails, or float the currents of the turbulent Colorado River.

If you haven’t seen it yet, the Grand Canyon surely deserves to be included on your “to visit” list.

By Claudia Miclaus