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Calcrete Field Trip 2023 - Hendricks Road at Eagle Lakes, WA

Revised interpretation - I am revising my interpretation of the brown, cemented sediments at Hendricks Road. These same beds rest atop Elephant Mountain basalt at Saddle Mountains making them part of the Ringold Fm. At Saddle Mts, they are overlain by a >20m-thick section of the Ringold sediments. The beds are also preserved in pockets of the flood-scoured scabland at White Trail (Quincy Basin) and likely lower Lind Coulee. At all locations, the brown alluvial beds were deposited in low order stream valleys established atop the basalt in post-Miocene time. At Hendricks Rd and White Trail, megafloods stripped away all overlying Ringold sediment that may have covered them (e.g., erosional remnants in a scabland surface). At Saddle Mountains, the alluvial beds lie at the base of the Ringold section. The Ringold and underlying basalt were tectonically elevated prior to arrival of megafloods and escaped scour. A thin diatomite indicates these beds were low in a valley in late Miocene-early Pliocene time. Bk horizons suggest rainshadow aridity was present, which arrived sometime after 7 Ma.

Directions - Drive 7.5 miles west on Hendricks Road from the Hwy 17-Hendricks Road intersection. Roadcuts are located a short walk downhill from the kiosk/public parking area for Bailie Memorial Youth Ranch and Wildlife Area, where Bailie Creek crosses the road. An unnamed pond to the west fills a scabland basin. Do not block gated driveways near roadcuts. Road shoulders are narrow.

GPS: 46.674414, 119.151598

Optional stop: Eagle Lakes scabland overlook - A serviceable overlook of the Eagle Lakes scabland is located 5.5 miles away, up the hill. Continue west on Hendricks Rd to Sagehill Rd. Turn R (north) on Sagehill. Turn R (east) on Eagle Rd. Road shoulder pullout is located just before road's end at private gate to Eagle Lakes Ranch Lodge. Walk short distance down the canal road for a better view.

Hendricks Road site - An anomalous remnant of bedded alluvium sits within a major scabland just downstream of a cataract. The brown beds do not appear to rest on a scabland surface, rather a pre-glacial stream channel incised in basalt. Floods from Othello Channels moved west and south across the map, exiting to Ringold Coulee and the Columbia Valley.

Improbable Outcrops - Three tidy roadcuts along Hendricks Rd at Bailie Creek expose a remnant island of bedded sediment atop the Eagle Lakes basalt. Five nondescript, gray-brown sandstone-mudstone beds composed of locally-derived basaltic sediment contain weathered basalt cobbles, fossil cicada burrows, and Bk soil profiles (Stage I-III caliche). The beds rest atop the 10.5 Ma Elephant Mountain basalt, one of the youngest flows in the CRBG, and show no evidence of being baked by an overriding basalt flow (not an interbed). A yellow-green zone of weathered basalt (20 cm-thick) occurs below the beds and atop hard basalt. The beds lie unconformably atop the weathered zone. Three beds have Bk soil profiles, the thickest of which is developed in the uppermost bed. Soil development and insect burrowing indicates time passed between the deposition of each bed. The dry cataract in the distance is now filled by an unnamed pond, the southernmost of the Eagle Lakes potholes.

Depositional setting - The brown beds are alluvial deposits a low order stream network draining the western Palouse Slope/Wahluke Slope and emptying to a broad, contiguous floodplain of the ancestral Columbia River. Pre-Wisconsin floodwaters appear to have removed most of the Ringold cover from atop the Elephant Mountain basalt with inititial scouring of the Eagle Lakes surface. Flooding here likely initiated hundreds of thousands of years ago. Flooding ceased for a time, then returned later during the Late Wisconsin (<20 ka, Missoula flood cycle), though routing of floodwaters may have changed (more from east, less from north).

Calcrete armor and Pliocene cicada - The fact that these fine-grained sediments, preserved immediately downstream of a sizable cataract now filled by a small lake, exist here at all is amazing. The sediments somehow escaped removal by repeated energetic megafloods flowing through Eagle Lakes-Ringold Coulee trough to the Columbia Valley. Were they protected by a bedrock knob that is now gone or were the hydraulics favorable to retaining them or did the calcrete function as an armor? The beds resemble brown alluvial sediments exposed at Lind Coulee, White Trail, and Saddle Mountains. Fossil cicada burrows indicate each bed dried out after it was deposited. Important to note that these are Pliocene cicada, not Pleistocene cicada. Pleistocene cicada fossils, which are very common and produce identical trace fossils, are closely associated with dryland sagebrush plant communities. Pliocene cicada are not often mentioned in literature of Eastern Washington (i.e., articles on Palouse Loess), but are helpful in understanding the region's paleoclimate between ~7 and 2.6 million years ago. A thicker caliche developed at the top of the stack than at lower levels; its likely Pleistocene. Today's water table is raised artificially by the Columbia Basin Irrigation Project, filling the nearby pothole lakes.

Bk horizons - Stage III caliche profile at top of Bed 5 indicates an age considerably older than the Missoula cycle. Beds below are Pliocene. There's a thin diatomite in the stack too, just off camera, discovered by Rene Barendregt in Sept 2023.

Weathered basalt clasts - Deeply weathered basalt clasts appear to be mostly colluvial (angular) and are not far traveled. The stream had rocky banks and colluvial clasts simply fell into the channel from time to time.

Pre-weathered or weathered in place? Pliocene streams likely encountered a weathered basalt surface on the way to becoming saprolite and entrained some bits of regolith.

Scabland evolution - Major flood coulees, scabland basalt surfaces (dark gray), and preserved remnants of Ringold Fm sediments (light gray) are shown in the map above. Mapped bodies of Ringold are typically several meters thick. Weak Ringold sediments floor lower Ringold Coulee and others in the area. Ancient floods seem to have followed a formerly contiguous north-south path from Drumheller Channels to Eagle Lakes-Ringold Coulee. That route was at some point cut off by later uplift of the Saddle Mountains anticline and/or deepening of Crab Creek Valley. Ancient floodwaters likely encountered a surface composed of both hard bedrock and saprolite with a thin loess cover. Black dots are my calcrete study locations.

Correlative deposits in Quincy Basin - At White Trail, a flood-cut, gravel-filled channel is incised into brown, cemented beds of alluvium identical to those exposed at Hendricks Road. The muddy sandstone beds are Pliocene Ringold. They contain fossil Bk horizons, cicada burrows, and curious pebbles of dark red opal. Bedding dips gently in both locations. The gravel at White Trail is a pre-Wisconsin flood deposit. A thick, flat-lying calcrete (Stage III+) - a bit thicker than at Hendricks Road - overprints both the flood gravel and the older alluvium. The calcrete armors a remant geomorphic surface hundreds of the thousands of years old, likely the same unit found at George Landfill, Winchester Wasteway, Paradise Flats, White Bluffs, and numerous other locations underlain by calcrete ledges.

Brown beds. I think the same brown beds occur at other locations atop Elephant Mtn basalt.

Saddle Mountains crest - Identical brown beds with cicada burrows occur atop a <1m-thick orange weathered zone with white, horizontal stringers that caps the Elephant Mountain basalt (10.5 Ma). This is the locally preserved base of the Ringold Fm. As much as 20m more Ringold section lies above.

Saddle Mountains crest - The brown beds have Bk horizons of similar thickness and developed to the same degree as at Hendricks Rd. The weathered zone, alluvium, and soil profiles parallel the surface on the underlying basalt.

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