Calcrete Field Trip - Hendricks Road at Eagle Lakes, WA (Revised Nov 2022)
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. They are overlain by a >20m-thick section of the Ringold sediments there. The beds are also preserved in pockets of the flood-scoured scabland at White Trail (Quincy Basin). At all three locations, the 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 represent the basal portion of the Ringold section. The Ringold and underlying basalt were tectonically elevated prior to arrival of megafloods and escaped scour.
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.
Hendricks Road site - An anomalous island-remnant of bedded alluvium sits within a major scabland just downstream of a cataract. Floods from Othello Channels moved west and south across the map, exiting to Ringold Coulee and the Columbia Valley.
Outcrop Summary - Three tidy roadcuts along Hendricks Rd at Bailie Creek expose an island bedded sediment atop the Eagle Lakes scabland surface. 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-II caliche). The beds overlied 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 either of a low order stream network draining the western Palouse Slope/Wahluke Slope or are shallow overbank deposits of a broad, contiguous floodplain at the confluence of the ancestral Columbia River and other large tributaries from the east. Pre-Wisconsin floodwaters appear to have removed most of the Ringold cover from atop the Elephant Mountain basalt and initiated scouring of the Eagle Lakes surface and Ringold Coulee downstream (>200 ka). Flooding ceased for a time, then returned later during the Late Wisconsin (<20 ka, Missoula flood cycle).
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 did the calcrete function as armor? These beds resemble dark brown alluvial sediments exposed at Lind Coulee, White Trail, and Saddle Mountains. Fossil cicada burrows indicate each bed dried out after it was deposited. Today's water table is raised artificially by the Columbia Basin Irrigation Project, filling the nearby pothole lakes. 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 5.3 and 2.6 million years ago.
Bk horizons - Stage II+ caliche profile at top of Bed 5 indicates an age considerably older than the Missoula cycle. Beds below are Pliocene.
Weathered basalt clasts - Deeply weathered basalt clasts appear to be both alluvial (rounded) and colluvial (angular). Gravels containing weathered clasts and capped by paleosols elsewhere in the Channeled Scablands are found in non-flood sediments (Plio-Pleistocene) and in ancient flood gravels (pre-Wisconsin).
Pre-weathered or weathered in place? The beds' brown color is due to an abundance of basaltic grains. Pliocene streams likely encountered a weathered basalt surface - on the way to becoming saprolite - and entrained some pre-weathered material. Alternatively, they arrived as fresh clasts and weathered in place since the late Miocene. Is there a visible difference in the depth of weathering higher or lower in the section?
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. Important exposures of the Pliocene-Pleistocene stratigraphy are shown as black circles. Calcretes indicate the first flooding of Othello Channels-Eagle Lakes Coulee-Ringold Coulee occured during the pre-Wisconsin. Ancient floodwater likely scoured a surface composed of hard bedrock, saprolite, and thin loess that was shallowly gullied by local streams.
White Trail - At White Trail, a flood-cut, gravel-filled channel is incised into beds of brown, cemented, alluvium identical to those exposed at Hendricks Road and the Saddle Mountains crest. The muddy sandstone beds are Pliocene Ringold. They contain fossil Bk horizons, cicada burrows, and curious pebbles of dark red opal. Bedding dips gently west into Potholes Coulee. The gravel is pre-Wisconsin flood deposit. A thick, flat-lying calcrete (Stage III+) - thicker and more advanced than at Hendricks Road - overprints both the flood gravel and the older alluvium, making both deposits pre-late Wisconsin in age. The calcrete armors a geomorphic surface hundreds of the thousands of years old, likely the same unit found at George Landfill, Winchester Wasteway, and other locations in the region.
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. Some 20m more Ringold section lies above.
Saddle Mountains crest - The brown beds have Bk horizons developed to the same degree as at Hendricks Rd. The weathered zone, alluvium, and soil profiles parallel the surface on the underlying basalt.
Links to Other Stops: