Numeric Ages of Grand Canyon Rocks

Photo of layered rock with cliffs and canyons in the distance.
Deposited 270 million years ago, during the Paleozoic Era - Early Middle Permian Period, the Kaibab Formation is the topmost rock layer at the Grand Canyon.

NPS photo.

Introduction—The Need for Numeric Ages

When someone’s objective is simply to learn how old a rock layer is, sorting through the technical geologic literature, the subdivisions of geologic periods, and the scientific names of microscopic index fossils, can be confusing. Most non-geoscientists will find a description of the Kaibab Formation as from the Permian Period not particularly meaningful, much less a description that involves a more specific fossil stage. Moreover, the intricacies of how geologists tell time by using both relative and radiometric dating techniques can add to the complexity.

Nevertheless, people generally understand a numeric age, such as the Kaibab Formation being 270 million years old. Therefore, numeric ages are essential when communicating geology to the public and to one another.

But finding such numbers in the scientific literature is not always easy. Some studies report only the stratigraphic age or the broad geologic era or period of a rock unit and do not use numeric ages, see Geologic Timescale and Geologic Dating Techniques. Moreover, scientific papers that do publish radiometric age determinations are not always clear about the geologic significance of these dates. For example, a radiometric date on zircon crystals found in an igneous rock measures the time when the rock (and the zircons within it) crystallized. But dates on zircon grains found within a sedimentary rock only provide a maximum age for the sedimentary rock since the grains themselves crystallized in an older igneous rock that was eroded to become a sediment source. Grains within a sedimentary rock inherently must be older than the rock itself.

Unfortunately, telling geologic time seems mysterious to many people without backgrounds in Earth science. Naturally, a non-geoscientist may wonder, “How do you know that?” when a geologist or park interpreter says, “That rock formed 270 million years ago.” To add to the confusion, both technical and popular literatures report a wide variety of numeric ages for Grand Canyon rocks. Further, popular accounts may not always utilize the most current research. For example, one publication may say that the Kaibab Formation is 270 million years old, while another says 255 million years old. The same inconsistencies arise for the other rock units in the park. People may be left wondering which are the correct (or best) ages and why. At worst, they may discount the scientific methods used to measure deep time. Geologists know that these changes reflect the scientific process itself. Scientists continually apply new research, dating methods, and critical analysis of previously published works to refine the understanding of the age of rock units.

Best Numeric Ages for Grand Canyon Rocks

This compilation of best numeric ages for Grand Canyon rocks serves important scientific purposes, particularly given ongoing research into the age of Grand Canyon rocks, the difficulty in determining the ages of many rock units, and Grand Canyon’s geologic significance.

The goal of this compilation is to provide a single list of updated numeric ages that users could apply consistently, thereby facilitating better comprehension of the geologic history and features of Grand Canyon. Research moves forward and the scientific excitement of obtaining new knowledge about old rocks is an important part of Grand Canyon’s geologic story.

These best ages still have limitations and are approximations in some ways given the complexities of how rocks form through time, and are subject to revision as our understanding of Grand Canyon geologic history improves.

The constraints on determining the best ages for each rock unit include the inherent limitations of the dating techniques used, the availability of datable material and/or fossils present in each rock unit, and the quality and quantity of relevant geological observations. In turn, scientific understanding of Grand Canyon geology and how dating techniques are used to obtain the age of rocks are part of the expert opinion also needed to ascertain the best numeric values.

Rock Set Group Formation Stratigraphic Age Numeric Age (Ma)
Layered Paleozoic Rocks Kaibab Formation Early Middle Permian 270
Toroweap Formation Late Early Permian 275
Coconino Sandstone Early Permian 280
Hermit Formation Early Permian 285
Supai Group Esplanade Sandstone Early Permian 290
Wescogame Formation Late Pennsylvanian 300
Manakacha Formation Early Pennsylvanian 315
Watahomigi Formation Early Pennsylvanian 320
Surprise Canyon Formation Late Mississippian 325
Redwall Limestone Late Early – Middle Mississippian 340
Temple Butte Formation Middle – Late Devonian 385
Tonto Group Frenchman Mountain Dolostone Late Middle Cambrian 500
Muav Formation Late Middle Cambrian 504
Bright Angel Formation Middle Cambrian 506
Tapeats Sandstone Middle Cambrian 508
Sixtymile Formation Early Middle Cambrian 510
Grand Canyon Supergroup Chuar Group Kwagunt Formation Walcott Member Neoproterozoic 729
Kwagunt Formation Awatubi Member Neoproterozoic 750
Kwagunt Formation Carbon Butte Member Neoproterozoic 753
Kwagunt Formation Duppa Member Neoproterozoic 755
Galeros Formation Carbon Canyon Member Neoproterozoic 757
Galeros Formation Jupiter Member Neoproterozoic 765
Galeros Formation Tanner Member Neoproterozoic 770
Nankoweap Formation Mesoproterozoic 775
Unkar Group Cardenas Basalt Mesoproterozoic 1,082
Dox Formation Mesoproterozoic 1,120
Shinumo Sandstone Mesoproterozoic 1,130
Hakatai Shale Mesoproterozoic 1,230
Bass Formation Mesoproterozoic 1,255
Bass Formation Hotauta Conglomerate Member Mesoproterozoic 1,255
Vishnu Basement Rocks Youngest granite Quartermaster granite Mesoproterozoic 1,375
Later granites / dike swarms Phantom granite Paleoproterozoic 1,662
Cremation pegmatite Paleoproterozoic 1,698
Zoroaster Plutonic Complex Horn Creek granite Paleoproterozoic 1,713
Ruby gabbro Paleoproterozoic 1,716
Trinity granite Paleoproterozoic 1,730
Diamond Creek granite Paleoproterozoic 1,736
Zoroaster granite Paleoproterozoic 1,740
Granite Gorge Metamorphic Suite Vishnu Schist Paleoproterozoic 1,750
Brahma Schist Paleoproterozoic 1,750
Rama Schist Paleoproterozoic 1,751
Oldest basement Elves Chasm pluton Paleoproterozoic 1,840

Ma = mega annum = million years ago
Diagram showing stratigraphic column of Grand Canyon rocks.
Figure 24. Stratigraphic column of rocks of the Grand Canyon region showing the three sets of rocks and major unconformities: Great Nonconformity (white line), Great
Angular Unconformity (red line) and Great Unconformity (black line). Fm = Formation; Ss = Sandstone; Ls = Limestone.

Complexities Related to the Geologic Meaning of Numeric Ages

The Elves Chasm pluton at 1,840 Ma (mega annum; million years old) is the oldest dated rock in Grand Canyon. The precision of this analytical measurement is within one million years; in other words, scientists are 95% sure that if they dated these same grains repeatedly using the same method (uranium-lead on zircon crystals), we’d get an age within a million years either side of 1,840 Ma. The accuracy of this date depends on not just the dating method, but also anything that may have happened to the grains to partially reset their geologic clock after crystallization. Fortunately, zircon crystals contain two different uranium isotope parents that decay at different rates to two different lead isotope daughters so that a single grain gives two independent dates that cross-check each other to produce highly accurate and precise ages.

But outcrops of the Elves Chasm pluton are geologically complex. Figure 9 shows that dark inclusions were surrounded by and hence are older than the main Elves Chasm magma, then both were cross-cut by younger dikes. Thus, for full disclosure, only the main magma body crystallized 1,840 ± 1 million years ago, not the older inclusions or the younger dikes.

Photo of an outdoor geology display.

Figure 9a. Specimen of the Elves Chasm pluton on the Trail of Time.
MPS photo by Michael Quinn.

Illustration showing details of minerals within a rock sample.

Figure 9b. Sketch of the Elves Chasm Specimen; gd indicates the lithology of the main pluton (granodiorite) shown in gray, older inclusions are in purple and the younger granitic dike is in red.
Illustration by Karl Karlstrom.

Challenges of Determining Numeric Ages of Sedimentary Rocks

Sedimentary units present a still different complexity in determining their best age. Sedimentary rocks are usually deposited over long time periods so a single number is technically not correct even though it is of use for characterizing ages of rock units. The Bass Formation was deposited as a lime mud in shallow seas and contains stromatolites, the oldest visible/macroscopic fossils in Grand Canyon (Figure 10). Its best age is 1,255 ± 2 million years ago based on a U-Pb radiometric age determination on a volcanic ash bed within this unit. But the Bass Formation is more than 328 ft (100 m) thick and undoubtedly took many million years to deposit.

Photo of an outdoor geology display.

Figure 10a. Specimen of the Bass Formation on the Trail of Time. This rock was deposited as a lime mud and contains the oldest fossils (stromatolites) in Grand Canyon. An ash bed within this formation was dated at 1,255 ± 2 Ma.
NPS photo by Michael Quinn.

Illustration showing detail of minerals in a sample boulder.

Figure 10. Sketch of the Bass Formation specimin on the Trail of Time.
Illustration by Karl Karlstrom.

Fossiliferous sedimentary rocks often have well-known stratigraphic ages although numeric ages are commonly not available. For example, the Redwall Limestone (Figure 11) contains a distinctive assemblage of fossils. These fossils and the use of fossil biozones and the International Stratigraphic Chart v 2020/01 indicate that the Redwall Limestone is late Early to Middle Mississippian in age (which is about 340 million years old). Again, the deposition of this unit likely occurred over a period of a few million years.

Photo of an outdoor geology display.

Figure 11. Redwall Limestone specimen on the Trail of Time.
NPS photo by Michael Quinn.

Illustration of fossils on the seafloor.

Figure 11b. Sketch of fossils found in Redwall Limestone specimen on the Trail of Time. Diverse marine fossils include crinoids (1,2), bryozoa colonies (6,8), bivalves (9), and snails (10) that help constrain its age.
Illustration modified from Stan Beus.

Illustration trail of time symbol.
Figure 1. The icon for the Trail of Time exhibit at the South Rim of Grand Canyon reflects a cyclic view of the interactions between time, rock, and erosion.

One portrayal of geologic time is shown in Figure 1. Rock Captures Time refers to the depth of geologic time, measured in billions of years, and the stories told by different rock units. Time Carves Canyon reminds us of the millions of years it took for the river and erosion to carve through rock to shape canyons and landscapes. Canyon Reveals Rock summarizes multiple time scales — the very old rocks exposed by the actively carving Colorado River in the walls of the relatively young Grand Canyon.

The Trail of Time

One prominent effort to make the geologic history of Grand Canyon and the age of the rocks exposed within it more relevant to the public is the Trail of Time, a geologic timeline exhibit near Grand Canyon Village (Figures 4 and 5). The Trail of Time follows the Rim Trail between Yavapai Geology Museum and Grand Canyon Village and affords spectacular vistas, interpretive panels, and has samples of Grand Canyon rocks to see and touch. Also, it is a memorable and accessible family hike.

Illustration map of the Trail of Time on the Grand Canyon's south rim.

Figure 5. Perspective view of the Grand Canyon Village area on the South Rim of Grand Canyon. The Trail of Time exhibit extends from Yavapai Geology Museum to the Village, and then to Maricopa Point. The numbers and colors refer to segments of the Trail of Time: 1 = Million Year Trail; 2 = Main Trail of Time; 3 = Early Earth Trail.

Bronze markers set every meter (a long step) along the trail represent one million years of Earth’s history. The 2,000 steps between Yavapai Geology Museum and Grand Canyon Village cover the last 2,000 million (2 billion) years, encompassing Grand Canyon’s rock record. Rock specimens were collected along the river and brought up to be placed at their age (their “birthday”) along the timeline. The Early Earth Trail extends beyond the village to Maricopa Point and the age of the Earth at 4,560 million years ago.

Photo of people strolling on an asphalt trail.
Figure 4. Visitors ponder geology, rock exhibits, and the views near the “time zero” portal on the main Trail of Time.

NPS photo by Michael Quinn.

The Trail of Time was funded by the National Science Foundation with in-kind support from Grand Canyon NP. It opened in 2010. The Trail of Time project was the culmination of 25 years of research on the geology of Grand Canyon and the age of its rocks by the Trail of Time team, and is still an active bridge between research advances and geoscience education.

Trail of Time Companion 2019

The Grand Canyon Trail of Time Companion, a book and walking guide to provide additional layers of information for visitors, was published in 2019. This recognizes the concept of multiple knowledge hierarchies that focuses on the learning journey of each visitor. Hence, the goal is to help each visitor move up the hierarchy from whatever their level of entry may be. The Companion also summarizes the making of the Trail of Time exhibit. And, in one section, the rock samples that are displayed along the trail provide a narration of Grand Canyon’s geologic history, told (as if) by the rocks themselves. The Companion incorporated new research on the age of Grand Canyon rocks, including revisions to the stratigraphy of the Grand Canyon Supergroup and the Paleozoic Tonto Group, as well as refinements to the ages and nomenclature of many rock units.

Previous Compilations of Numeric Ages

The first systematic compilation of best numeric ages was issued in 2005 in the then-Grand Canyon NP publication Nature Notes. While the authors did not conduct geologic research themselves, they extensively consulted with geoscientists investigating Grand Canyon’s geology and reviewed the technical literature in order to prepare their compendium. The Nature Notes compilation did not include specific ages for every rock unit exposed in Grand Canyon, but provided numeric ages or range of numeric ages for most of the canyon’s prominent units.

These numeric ages were also published in Park Science and Boatman’s Quarterly Review, a publication of the Grand Canyon River Guides. They were also presented to the public in park-produced publications and in ranger interpretive programs, and used elsewhere such as in the Yardstick of Geologic Time. The compilation was superseded by the National Park Service Natural Resources Report Telling Time at Grand Canyon National Park: 2020 Update and this series of web articles.

Learn More

Tiny image of the cover of a report titled Telling Time at Grand Canyon National Park.

To learn more about the age of Grand Canyon’s rocks, please see:

Karlstrom, K., L. Crossey, A. Mathis, and C. Bowman. 2021. Telling time at Grand Canyon National Park: 2020 update. Natural Resource Report NPS/GRCA/NRR—2021/2246. National Park Service, Fort Collins, Colorado. [IRMA Portal]

Photos and Illustrations

Part of a series of articles titled Telling Time at Grand Canyon National Park.

Grand Canyon National Park

Last updated: March 12, 2024