top of page

Ancient Flood Gravel Beneath a Thick Calcrete Ledge - White Bluffs, WA

Exotic clasts in gravel. An exotic clast-bearing conglomerate at White Bluffs Overlook was left by an ancient Ice Age flood. The post-Ringold unconformity appears to be a sequence-bounding surface that may correlate with a late-Neogene unconformity in the Rocky Mountains.

Flat-lying Pliocene Ringold lake beds (<5 Ma) are unconformably overlain by a meter-thick conglomerate composed of subangular calcrete rip-ups mixed with exotic clasts (granite, schist, andesite, quartzite). The conglomerate is Pleistocene age, likely a bit younger than 1.5 Ma. Exotic clasts derive from outside the Columbia Basin; they were brought here from the north and east by a combination of ancient rivers (ancestral Columbia, Salmon-Clearwater Rivers) and Ice Age floods. Some of the sediment dropped here by those rivers was later reworked by the cataclysmic floods. Wise not to assume that every exotic clast in Columbia Basin was swept here by floods from western Montana or from beneath ice sheets in British Columbia. Clasts may be reworked from older, local deposits or might be from less-exciting Idaho.

The post-Ringold unconformity is the local expression of a region-scale boundary that separates two of Washington's major packages of rocks, called synthems (unconformity bounded sequences). The erosional surface separates High Cascades Synthem rocks (<3 Ma) above from Walpapi Synthem rocks (13-7 Ma) below (Sloss, 1963; Armentrout, 1987; Cheney, 2016). Four Cenozoic synthems are recognized in the state. The surface has not been precisely dated, but it truncates the youngest Ringold sediments, thus appears to be no older than ~3.2 Ma and no younger than ~1.5 Ma (approximate onset of Ice Age conditions in Washington). If a regional surface, its tied to region-scale tectonism (~7 Ma to ~3 Ma), which is not well understood.

Field notes. My field notes from a previous visit to a different outcrop in the White Bluffs. If you have ever wondered what Field Geologists do, you can bet sketching and describing layered strata is part of the job. All of the great geologists were pretty good to great sketch artists. A tradition to keep.

Unconformably overlying the conglomerate is a meter-thick, Stage V calcrete paleosol with blocky morphology. Thick calcretes require 10,000s-100,000s years to form, which makes the underlying conglomerate, which I interpret as an "ancient" Ice Age flood deposit (flood gravel), more than 100,000 years old. Likely its much older.

Bedded gravel composed of calcrete clasts. Foreset bedding in the exotic-bearing gravel. Most of the clasts you can see are chunks of calcium carbonate, ripped up from an older paleosol, but there are plenty of exotics in there, too. South is to the right.

Calcrete rip-ups and exotic lithologies. A variety of pebbles with exotic lithologies are fairly easy to find, though their proportion is small compared to the calcrete clasts.

The "ancient" outburst flood record (pre-Missoula floods cycle) in Eastern Washington is not well preserved, but if you develop an eye for it, you'll find it in numerous places. These so-called pre-Late Wisconsin deposits generally include weathered flood-laid sediment, flood-cut surfaces, interfingering loess, and paleosols. The exotic-bearing gravel shown here grades laterally into reworked silty-sandy deposits nearby, also with abundant rip-ups.

A page from my book. The first draft of any project begins with a sketch.

Capping calcrete. Ringold Fm and calcretes are well exposed along the Old Ringold Road grade at the White Bluffs Overlook.

Over the decades, busloads of geologists have visited the White Bluffs Overlook. Most just enjoy the view of the Hanford Reach, the impressive landslides, and the moth-balled nuclear reactors across the river. Geologically speaking, there is a lot to see here though the overgeneralized guidebooks and bland interpretive signs give it short shrift. Beautifully preserved sediments in accessible roadcuts are located just down the hill, along the Old Ringold Road hiking trail. The sediments of the Ringold Formation are challenging and require geologic chops to appreciate the details. And its the details that matter.

Detailed stratigraphice descriptions in guidebooks on Washington's geology are notably rare. Other states do it differently. The Wyoming Geological Association and TRGS's Northwest Geology journal, for example, often publish original, detailed content in their guidebooks. Those authors, those editors don't fear being too technical for the audience. In fact, they often highlight the details and in doing produce important publications that remain relevant for decades.

Non-technical readers can just skip over the details, can't they? It costs them nothing. Editors and publishers should not dumb down the geology for the general public. At some point, its no longer geology, no longer STEM.

One problem seems to be a reluctance on the part of authors to do new field work. Detailed geology requires an author go find something new and write down what they found. But new work opens an author up to criticism that he might just as well avoid, if sensitive. The best geologists write bold and clear. We were trained to lead, right?

My suggestions to the next generation of Columbia Basin guidebook authors, editors, and publishers:

1.) Include stratigraphic details in site descriptions. Original work, first hand strat columns illustrated well.

2.) Reduce the number of pages describing the majesty of the landscape. More geology, less nature appreciation.

3.) Stop revisiting the places Bretz worked. There are plenty of important, photogenic outcrops he never found or considered.

4.) Hire authors from Gen X or younger. Too many scabland geology tours today are led by retirees for retirees.

Time to move the Missoula Floods narrative forward with new discoveries and new details. The familiar old tales have grown stale. Field trip leaders need to stop making the same loops. Professors need to start dragging students out to far-flung valleys in search of something new again. Try this. Next time you visit one of the famous stops in the Channeled Scablands, endeavor to discover something new, something small, some detail that no one wrote about 50 years ago. You almost certainly will. Make a sketch and show it to others.

Go somewhere new: Ringold Road Bluffs Hike lies near the southern trailhead of the Old Ringold Road trail. The place gets hot as hell in Summer, so plan your shoulder season trip accordingly. Click below for larger PDF of the map above.

Ringold Rd Bluffs Hike Map
Download PDF • 9.82MB

North and south trailheads. The two White Bluffs field stops are located at opposite ends of the Old Ringold Road hiking trail, which is gated at both ends. Access the White Bluffs Overlook from gravel road leading south from Hwy 24. Turnoff is between Othello and Mattawa. Access the Ringold Road Bluffs Hike from Taylor Flats Road and Ringold Road north of Pasco.

Reconstructed profile. Topographic profile (top) of the White Bluffs between Savage Island and Kennewick, WA reconstructed by me in Google Earth and Adobe Illustrator. Ringold Road Bluff Hike and numbered fossil study localities in the Ringold Formation are shown (Brown & McConiga, 1960; Gustafson, 2012, 2015).

Honest work. The original profile and cross section by Brown & McConiga (1960, Fig. 1) contains considerably more information and the locations of wells and field-measured stratigraphic sections by Russell, Merriam & Buwalda, McKnight, Glover, Newcomb & Strand, Jenkins, and USBOR. I count this among the best of the pre-WWII reports on Eastern Washington geology. It is short, authored by field geologists, and descriptive (i.e., useful). The information presented is plainly developed from the geologists' field notes. There is no easy chair speculation here. The authors show what they know and reveal what they are struggling with. How often do you see such direct reporting in geoscience publications today?

New geology. Cemented clastic dikes, a huge active landslides, thick calcrete ledges, and other cool stuff are yours for the viewing on the Ringold Road Bluffs Hike. Left: Unsheeted, wedge-shaped clastic dikes intrude downward into siltstones of the upper Ringold Fm (Savage Island Member). The dikes are truncated by a calcrete gravel deposited by an energetic current (ancient flood? mass wasting? something else?). Look for deformation at the contact between the gravel and siltstones (load casts and flame structures). Similar deformation is found at the same stratigraphic positon at Coyan Rd, White Bluffs Overlook, and exposures east of Danielson Rd. Right: Many road sign artists secretly want to be Geologists. Prisons need geologists, too, you know.

Stratigraphy at the rim of White Bluffs. Notes from my field book (May 2021). I see 2 prominent calcrete ledges (paleosols) with blocky morphologies and an even older calcrete from which the gravel was derived. The gravel was either deposited by an overland flood moving southwest from near Othello toward the Columbia Valley (prior to incision of White Bluffs/Hanford Plain) or by a local, low-angle, subaqueous(?) slide into Hanford Reach (some relief and a high energy flow required). Because I've found evidence of pre-Wisconsin flooding at WBO, Herman Railcut, and elsewhere in the area as well as identical deformation at the same stratigraphic position in exposures both north and south of Saddle Mountains, I favor a flood origin for the gravel. Eastern nose of the Saddle Mountains anticline may have grown a bit since its deposition. Hike up there and see for yourself. Let me know what you discover.

Caprock. Cemented sediments with pedogenic calcrete paleosols unconformably overlie upprt Ringold lakebeds along the rim of White Bluffs. The petrocalcic horizons did not develop high on this dry, airy blufftop; it did so on a broad, low plain prior to incision of the Hanford Plain by Ice Age megafloods.

Gravel. Ringold siltstones are truncated along a prominent erosional surface by a gravel composed of calcrete rip-up clasts. Is there evidence supporting a specific high-energy process capable of transporting these large, low-density clasts? What possibilities exist? Is this even a gravel? How much time is represented by the unconformity?

Questions for students. Load structures occur at the contact between Ringold and the overlying gravel, but not everywhere. If you traverse a few hundred meters north or south along the bluff, the deformation goes away. What might confine the lateral extent of deformation? What relief or lack of relief existed in the landscape at the time deformation occurred? Did the White Bluffs exist then? How do crosscutting relationships constrain the age of the deformation? Was the upper Ringold brittle or ductile when deformed? What was the geologic setting that best explains the upper 10m of stratigraphy at the blufftop? Is there a connection between White Bluffs Overlook and Ringold Road Bluff?

Deformed lakebeds. Private orchard land along White Bluffs off Sagehill Rd. Contorted bedding near top of Savage Island section is continuous over tens of meters distance. Nature and age of sediment immediately above deformed zone changes.

Last 50 Posts
All Posts by Month
    bottom of page