Calcrete Field Trip - Hendricks Rd
Directions - Drive 7.5 miles west on Hendricks Road from the Hwy 17-Hwy 260/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
An overlook of Eagle Lakes Coulee and scabland is located 5.5 miles away. Continue west on Hendricks Rd to Sagehill Rd. Turn R (north) on Sagehill. Turn R (east) on Eagle Rd. Informal roadside overlook is located just before road's end at private gate to Eagle Lakes Ranch Lodge.
Hendricks Road site - Note where sediments sit in the scabland topography. Floods moved west and south across the map.
Outcrop Summary - Three roadcuts at Bailie Creek expose old sediments deposited atop the Eagle Lakes scabland surface. Five nondescript, gray-brown mudstone beds composed of locally-derived sediment contain weathered basalt cobbles, fossil cicada burrows, and Bk soil profiles (Stage I-II caliche). A yellow-green zone of weathered basalt (20 cm-thick) occurs below the beds and atop unweathered basalt. The weathered zone either began to form immediately after coulee cutting (i.e., the loose material was not stripped away by floodwaters) or formed more recently beneath a pothole lake (Holocene). The mudstone beds appear to lie unconformably atop the weathered zone. Three beds have Bk soil profiles, suggesting time passed between deposition of each. The top bed has the most prominent Bk horizon. Are they backflood rhythmites? The fact that these fine-grained sediments exist here in a flood-scoured scabland is amazing. Floodwaters rushed across this location during initial cutting of the coulee (Time 2) and during later flood events (Time 4). Columnar basalts form walls of a dry cataract now filled by an unnamed pond, the southernmost of the Eagle Lakes.
Stratigraphy - Cicada burrows indicate the beds remained dry and above the water table after they were deposited. Today's water table is raised artificially by the Columbia Basin Irrigation Project. The beds may be flood rhythmites, but their appearance is quite different than most Touchet Beds, which are typically light-colored and micaceous. While the Bk horizons that overprint the upper two beds may be late Pleistocene in age (Time 4), the scabland surface below is older, perhaps middle Pleistocene (Time 2).
Beds escaped erosion - Cemented sediments containing weathered basalt clasts, lying atop scabland, and capped by a caliche horizon somehow escaped removal by energetic megafloods flowing south and west through Eagle Lakes Coulee. These beds may be correlative with dark brown, alluvial sediments at the O'Sullivan Dam/Lind Coulee Fault stop. This exposure, at Bailie Creek, is located immediately downstream of a cataract, now filled by a small lake. View is to the NE.
Just how old is the Eagle Lakes scabland surface?
Was it first scoured by pre-Wisconsin floods and later by Missoula floods?
Bk horizons - Stage II+ caliche profile at top of Bed 5 indicates an age considerably older than the Missoula cycle. The Missoula floods, if they followed this route, did not remove all of the sediments.
Weathered Basalt Clasts - Deeply weathered basalt clasts may be colluvial, but rounding suggests they were deposited by flowing water. Weathered clasts elsewhere in the Channeled scabland have been used to distinguish pre-Missoula flood deposits.
Scabland surfaces and Ringold remnants near Othello - Named flood coulees, scabland basalt surfaces (dark gray), and preserved remnants of Ringold Fm sediments (light gray) are shown with Ice Age flood routes (arrows) and important exposures of the late Pliocene and early-middle Pleistocene stratigraphy (black circles).