General Geology
Correlation

Rocks of similar age and composition to those of the Ootsa Lake group
are present in several parts of British Columbia, particularly east of and
parallel with the Coast Mountains.

In the vicinity of Whitesail Lake area rocks of the group have been found
in Nechako River map-area to the east (Tipper, 1955), Fort St. James map-
area (Armstrong, 1949), and Houston map-area (Lang, 1940) to the north.
Tipper (personal communication) finds similar rhyolites in Anahim Lake map-
area to the southeast.

In southern British Columbia the Kamloops and Princeton groups, which
include sedimentary and volcanic rocks of Tertiary age, may be in part
correlative. The Kitsilano group, though in part correlative in age, is largely
of sedimentary composition. In the Chilcotin area and east of Taseko Lake
rhyolites and conglomerates occur (Logie, 1929, p. 253) that may be of
similar age.

In McConnell Creek map-area of north-central British Columbia the
Sustut group (Lord, 1948, p. 34) of Upper Cretaceous and Paleocene age
may be correlative. Though the Sustut group is composed largely of continental
sedimentary rocks it does contain some beds of dacitic tuff.

Oligocene or Later Volcanic Rocks

The youngest consolidated rocks in the map-area are relatively flat-lying
basaltic flows and related tuff and breccia that overlie unconformably the
Ootsa Lake group. Associated with these rocks is a fresh-looking gabbro dyke
that may be an intrusive phase of the basalts. No fossils were found in these
rocks but they are similar to other basalts present in adjacent areas that are
considered to be late Oligocene or younger in age. In Fort St. James and
Nechako River map-areas similar rocks are referred to as the Endako group.

Distribution

The largest exposures of these rocks in the area are around Fenton Lake
and the southwest shoulder of Chef Ridge. Near the headwaters of St. Thomas
River they form a distinct escarpment about 800 feet high. In the northeast
corner of the map-area they are widespread and form the southward extension
of a large area of similar rocks in the Houston area to the north. They occur
on the Mosquito Hills, the eastern tip of Whitesail Range, and as numerous
small outliers east of the Quanchus Range. On the north shore of Eutsuk

73