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Old Maid Coulee Site Geology - Connell, WA

The Old Maid Coulee site, located near Connell, WA, contains convincing evidence of "pre-late Wisconsin" flooding. Geologists distinguish deposits from the more voluminous and better-studied Missoula floods (18-14 ka), which are "late Wisconsin" age, from those left by older floods, we call "pre-late Wisconsin" floods or sometimes "ancient floods". The older flood record is thinner, somewhat ambiguous, and contains conspicuous calcic paleosols (caliche, calcrete), which attest to its antiquity. Unlike evidence for the Missoula floods, which is found in thousands of roadcuts, railcuts, and streambanks throughout the Columbia Basin, evidence for ancient flooding is widely scattered and not all that spectacular. Its subtle and often "indirect" (Spencer and Jaffee, 2002).

There really isn't that much descriptive detail to be found in the reports, so I visited the site myself and described what I found. My field notes from my January 2021 visit are shown above.

The Old Maid Coulee site is one of about 20 locations in the region discovered by pre-WWII reconnaissance geologists. Its geology was formalized in articles by J Harlan Bretz and Vic Baker. That list of 20, best presented in Coppersmith et al. (2014, Appendix E, p. 4.11), is provided below as a PDF.

Coppersmith et al 2014 Appendix_E_excerpt
Download PDF • 62KB

I've visited all the remaining, accessible sites on the list. Several of the exposures are quite diminutive and were never very convincing. Others have been mined out or lost to development. Old Maid Coulee is still in good shape and worth a visit. But like all of the pre-late Wisconsin sites in the Channeled Scabland, the geology here won't smack you in the face. Its not bombastic, colossal, catastrophic, monstrous, or stupendous. Its small geology. Its about the details. Its real geology.

The framework elements at Old Maid Coulee include:

1.) OLD GRAVEL & CALCRETE. Cobble gravel with south-dipping foresets (old flood gravel) with reversed magnetic signature (>780 ka) and capped by an advanced-stage calcrete (paleosol) that overprints the gravel and probably a skiff of loess (tentatively dated >350 ka). Pre-late Wisconsin.

2.) DIAMICT & NODULAR LOESS. Pebbly, silt matrix diamict that unconformably overlies the calcrete and grades upward into modestly-cemented L2 nodular loess (paleosol). The nodular texture in the loess is created by thousands of backfilled feeding burrows of cicada nymphs (trace fossils).

3.) TOUCHET BEDS. Several thin, uncemented, and silty flood rhythmites (Touchet Beds, reworked loess) left by late Wisconsin Missoula floods. Late Wisconsin (<20 ka).

Timescale terminology associated with the Ice Age floods is often tedious and confusing. A real turn off. But if you can commit a few important dates to memory, things get a lot more fun. The dates in bold text are important. Hope this figure helps.

Other locations where thick calcretes and evidence of ancient flooding are found. Those in blue are my current research sites. Headless Old Maid Coulee is located on the western Palouse Slope, south of the intersection of two much larger coulees, Washtucna Coulee and Esquatzel Coulee. The texture of the landscape changes to the east of the site (loess-covered Palouse Hills) and west of it (flood-scoured Pasco Basin).

Platy calcrete, up to ~75cm thick, pinches laterally across the exposure.

OMC is a humble borrow pit off Blanton Road. The steep south side and flat floor of Old Maid Coulee in the distance. View is to the SW. Floodwater flowed away from the camera.

The Old Maid Coulee Site is a good-sized borrow pit that sits quietly along a particularly lonesome stretch of Blanton Road. The sinuous namesake coulee winds its way through ag fields and CRP ground. Floods flowed toward the camera.

Flint (1937, p. 538) provides this description of the site:

Old Maid Coulee - A pit at 1050 feet A.T., in the NE1/4 NE1/4 Sec. 24, T 13 N, R 31 E, on the north slope of Old Maid Coulee just west of U.S. Highway 395, exposes Touchet beds resting unconformably on an older deposit through a horizontal distance of nearly 100 feet. The older deposit has a B horizon consisting of 3 to 5 feet of calichified silt and firm pure caliche. This horizon is underlain by gravel with subordinate sand. The gravel is granule, pebble, and cobble size, with a few boulders up to 3 feet in diameter. It is all angular to rounded basalt, except about 2 percent of the pebbles, which are rounded fragments of greenish chal­ cedony, vein quartz, caliche, “Palouse soil”, and a single grayish white quartzite. The sand includes zones of coarse basaltic fragments and other zones of medium to fine quartzose sand, including micas, feldspars, and other products of crystalline rocks. The deposit as a whole is strati­ fied in courses of beds foreset southwest down the coulee.

Let me know what you find at Old Maid Coulee:


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