Pg. 18 (fig. 8). Tshirege Member of Bandelier Tuff of Tewa Group. A welded rhyolitic tuff composed of small fragments of crystallized pumice and crystals and crystal fragments of sanidine and quartz in a welded tuff matrix. Thickness 100 to 200 feet near eastern margin of area [Los Alamos]; about 1,000 feet at head of Rito de los Frijoles in southwestern part of area. Rests with erosional unconformity on all older rocks with which it is in contact. On Pajarito Plateau rests on Otowi Member (new) and fills eroded channels in that member. Overlaps Otowi Member to west and rests on Tschicoma Formation in the Sierra de los Valles. Also, in the Sierra de los Valles, the Tshirege Member laps onto some of Cerro Toledo Rhyolite (new) domes. Age is Pleistocene.
Type area: Pajarito Plateau and adjacent lower slopes of the Sierra de los Valles, Los Alamos area, north-central NM. Named from exposures in vicinity of Tshirege ruins, in NW/4 sec. 5, T. 18 N., R. 7 E., where member forms capping rock over large area of Pajarito Plateau. Small outliers cap mesas as far east as Puye Escarpment.

Source: US geologic names lexicon (USGS Bull. 1350, p. 775).

Informal upper and lower members of Bandelier Tuff (following usage of Smith and Bailey, 1966) dated by K-Ar method on anorthoclase and sanidine samples taken in Valles caldera, Jemez Mountains, Sandoval Co, NM in San Juan basin. Lower member--called the Otowi Member, and underlying Guaje Member by Griggs (1964)--dated on sanidine as 1.4 m.y. old. Upper member--called the Tshirege Member by Griggs (1964) --dated on anorthoclase and sanidine as 1.0 m.y. old. [Note that the author uses "upper member", not "Tshirege Member", as geologic name --however, Tshirege is inferred.] Has reversed magnetic polarity. Is of early Pleistocene age.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Bandelier Tuff of Tewa Group, previously divided informally into "upper" and "lower" members, revised and divided into two formal members: 1) Otowi Member (at base), whose lower contact is extended to include the basal pumice fall, Guaje Member of Griggs--reduced in rank to Guaje Pumice Bed--and the overlying unnamed ash-flow units (Otowi Member of Griggs); and 2) Tshirege Member (at top), which includes a basal pumice fall, Tsankawi Pumice Bed (new), and the overlying unnamed ash-flow units (Tshirege Member of Griggs). Ash-flow units not formally named in either member. Is in Jemez Mountains, Sandoval Co, NM in San Juan basin. Is of Pleistocene age.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Pg. 38 (fig. 11), 39 (table 10), 40 (table 11). Tshirege Member of Bandelier Tuff. Reported K-Ar ages of Doell and others (GSA Mem. 116, 1968) are recalculated using new decay constants of Steiger and Jager (1977). Age of Tsankawi Pumice Bed is 1.12 +/-0.03 Ma; overlying ash flows, 1.02 +/-0.04 Ma and 1.05 +/-0.04 Ma.
Notable localities (Tsankawi Pumice Bed) in Taos SW 7.5-min quadrangle, Taos Co., and Dalles 7.5-min quadrangle, Valencia Co., north-central NM.

Source: Publication.