Pond Ridge Rhyolite. Unit is part of sequence of Precambrian volcanic rocks associated with Taum Sauk caldera in western part of St. Francois Mountains, southeast Missouri (Midcontinent region). Notable exposures on Pond Ridge, north slope of Russell Mountain, [unnamed?] ridge between Russell Mountain and Pond Ridge, and Shepherd Mountain Lake dam. Consists of dark-maroon to grayish ash-flow tuff containing up to 20 percent white to pinkish feldspar phenocrysts, few quartz phenocrysts and many large, reddish fiamme. Thickness 130 m. Overlies Cedar Bluff Rhyolite (new); underlies Buck Mountain Shut-ins Formation (new). Age is Precambrian. Report includes geologic map. Unit named and described on stratigraphic column (table 1).
Pond Ridge Rhyolite replaces: Middlebrook Group (Russell Mountain) and Stouts Creek Rhyolite (Buck Mountain, Pond Ridge, and Shepherd Mountain Lake) as mapped by Tolman and Robertson (1969, Missouri Geol. Survey Rpt. Inv., no. 44); upper part of undifferentiated felsite of Anderson (1970, Missouri Geol. Survey Rpt. Inv., no. 46), and Unit 715 of Berry and Bickford (1972, Bull. Volcanology, v. 36, p. 303-318).
Type section: in NE/4 NW/4 sec. 3, T. 33 N., R. 3 E., Ironton quadrangle, Iron Co., MO. Origin of name not stated by author, but probably named from ridge south of Graniteville, Iron Co., MO.

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

Pond Ridge Rhyolite, 3rd formation from base (of 12) of /Taum Sauk Group (new) of /St. Francois Mountains Volcanic Supergroup (revised). Study area is St. Francois Mountains, southeast Missouri (Midcontinent region). Overlies Cedar Bluff Rhyolite (revised) of Taum Sauk; underlies Buck Mountain Shut-ins Formation (revised) of Taum Sauk. Age is Precambrian Y. Nomenclature listed in table 1.
[Conflicts with nomenclature guidelines (ACSN, 1970; NACSN, 1983, 2005, 2021): name Taum Sauk used for both group and formation within it (Taum Sauk Rhyolite has priority); name St. Francois Mountains applied concurrently to two different units in same area; a [supergroup] name combines a geographic name with the term ["supergroup,"] and no lithic designation is included.]

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

Pg. 228. Pond Ridge Rhyolite of Taum Sauk Group of St. Francois Mountains Volcanic Supergroup [Conflicts with several articles in nomenclature code guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021)]. Robertson (in Thompson, 1995, Missouri Div. Geol. and Land Survey, v. 40 (2nd ser.) revised, p. 10) stated "The presence of many large, reddish flamme is a distinguishing characteristic of the Pond Ridge Rhyolite. It is a dark maroon to gray ash-flow tuff containing up to 20 percent white to pinkish feldspar phenocrysts and a few quartz phenocrysts in addition to flamme. It is approximately 400 [feet] thick." R.E. Anderson (1962, unpub. PhD dissert., Washington University -St. Louis) had included these rocks in the upper part of his "Cedar Bluff felsite".

Source: Publication.