Chapter III, Pasco basin studies, p. III-8 (table 1), 19 (table 2), 30-32. Sentinel Bluffs sequence (informal) in Grande Ronde Basalt of Yakima basalt subgroup [informal] of Columbia River Basalt Group. Consists of at least 13 flows (includes Museum and Rocky Coulee flows); locally contains thin, discontinuous interbeds. Flows are generally black-gray, aphyric, and fine-grained; are high MgO chemical type. Average thickness 895 feet (272 m). Overlies Schwana sequence (informal; in Grande Ronde Basalt); contact is called "MgO horizon" which can be traced in subsurface and surface throughout basin. Lies below Vantage Member of Ellensburg Formation. Has norrmal polarity. Source area east of Pasco basin. Age is between 15.4 and 14.5 Ma [middle Miocene].
Type locality: along Sentinel Bluffs on east side of Columbia River at Sentinel Gap, in Saddle Mountains, [in secs. 10 and 15, T. 15 N., R. 23 E., Beverly 7.5-min quadrangle, Grant Co.], Pasco basin, central southern WA].
[Yakima basalt subgroup considered informal and should not be capitalized. "Subgroup" not recognized as a formal stratigraphic rank term (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021).]

Source: Publication.

Pg. 23 (fig. 1), 36-37, 38 (table 2), 43. Sentinel Bluffs unit (informal) in Grande Ronde Basalt of Columbia River Basalt Group. Consists of 8+ flows; rarely phyric to phyric with plagioclase phenocrysts, blocky to columnar. Has normal magnetic polarity (is youngest of N2 magnetostratigraphic units). = Wright and others' (1973) high-MgO chemical type. Is top unit of Grande Ronde Basalt. Lies above and interfingers with Slack Canyon unit (informal). Age is middle Miocene; isotopic age of 15.6 Ma.
Named from excellent exposures along Sentinel Bluffs at Sentinel Gap in Saddle Mountains, [Grant Co., central southern WA] (following Myers and others, 1979, Richland, WA, Rockwell Hanford Oper. Rpt., no. RHO-BWI-ST-4, 326 p.).
Reference localities: (1) Sentinel Bluffs on east side of Columbia River at Sentinel Gap, in Saddle Mountains, in SE/4 sec. 10, T. 15 N., R. 23 E., Beverly 7.5-min quadrangle, [Grant Co.], Pasco basin, central southern WA [=type locality]; (2) Columbia Hills water gap (Ortley anticline), in secs. 5 and 6, T. 2 N., R. 13 E., Dalles North 7.5-min quadrangle, [Klickitat Co.], southern WA; and (3) Mt. Zion quarry above WA State Hwy. 14, in NE/4 sec. 9, T. 1 N., R. 5 E., Bridal Veil 7.5-min quadrangle, [Skamina Co.], southern WA.

Source: Publication.

Sentinel Bluffs Member of Grande Ronde Basalt of Columbia River Basalt Group. Formal proposal. Is the youngest member of the Grande Ronde. Consists of fine- to medium-grained pahoehoe-like flows. Subdivided into (descending) Museum, Spokane Falls, Stember Creek, Airway Heights, California Creek, and McCoy Canyon flow groups. Overlies either Umatanum Member or Winter Water Member, both of the Grande Ronde. Underlies Vantage horizon, a hiatus in volcanic activity, and the distinct, plagioclase-phyric lava flows of the Wanapum Basalt of Columbia River Basalt Group. Age is middle Miocene (about 15.5 Ma).
See also Reidel and Valenta, 2000, Preliminary chemistry, petrology, and paleomagnetic data for the Sentinel Bluffs Member, Columbia River Basalt Group, Battelle Pacific Northwest Laboratories Report PNWD-3063 [informal report].

Source: Publication.