Precambrian rocks in the Tusas Mountains
— Reinhard A. Wobus

The stratigraphic interpretation of the Proterozoic metavolcanic rocks
and the quartzite—conglomerate sequence in the Tusas Mountains has
been the subject of considerable controversy. For a summary of these
interpretations see Wobus (this guidebook); the ensuing discussion fol
lows the interpretation of Burns and Wobus (1983), Gresens and Stensrud
(1974), and Just (1937), with an alternative interpretation to be found
in Barker (1958).

Kiowa Mountain, to the south of this stop, is the southeastern end
of a conspicuous ridge underlain by Proterozoic quartzite and quartzpebble
conglomerate that extends northwest into the Brazos Peak 15-
min quadrangle, where the same rock underlies Brazos Box. These
quartzites, and correlatives trending northwest from the Ortega Mountains
and from Jawbone Mountain, are preserved in the troughs of major
synclines, as recognized by Gresens and Stensrud (1974).

The quartzites are underlain by interlayered, metamorphosed, bimodal
volcanic rocks and their associated volcaniclastic sediments. The
mafic units of this assemblage (tholeiitic metabasalts, chlorite—muscovite
phyllite, and schist) were named the Moppin Metavolcanic Series
by Barker (1958), and the felsic components (metarhyolite sills and
ash-flow tuffs, quartz—muscovite schist, and minor fluviatile conglomerate)
constitute the Burned Mountain Metarhyolite, a name expanded
from Barker's original (1958) definition.