General Geology

Although the faunule does not permit a certain correlation, an upper Cretaceous
age is suggested.

From the foregoing, an Upper Cretaceous or Paleocene age is suggested. These
collections provide a lower age limit for the andesite unit of the Ootsa Lake Group.

In Fort St. James area, Armstrong mapped three units that together are
equivalent to the Ootsa Lake Group but singly are not correlative with either unit
of the group in Nechako River area. A few fragmentary fossils from the oldest unit
were dated as Upper Cretaceous or later (Armstrong, 1949, p. 70). Several col-
lections of fossil leaves from a sedimentary unit lithologically similar to sediments
of the rhyolite unit indicated Eocene or Oligocene age for the sediments.

Although the evidence is inconclusive, the Ootsa Lake Group may be as old as
Upper Cretaceous or as young as Oligocene. The evidence also suggests that the
andesite unit in the main may be definable as Upper Cretaceous or Paleocene and
the rhyolite unit as Eocene or Oligocene.

Rocks similar in all respects to the Ootsa Lake Group occur in Whitesail Lake
map-area, the type area (Duffell, 1959, p. 67), in Fort St. James area (Armstrong,
1949, pp. 68-74), in Anahim Lake area (Tipper, 1957), in Carp Lake area
(Armstrong, Hoadley, and Tipper, 1949), and in Quesnel area (Tipper, 1959b).
From a cursory examination of outcrops in areas adjacent to these it may be con-
cluded that lithologically similar assemblages are widespread but not continuous
or locally extensive throughout central British Columbia. In the Sustut Group
of McConnell Creek area, Lord (1948, pp. 36-41) reported dacitic tuff of
Paleocene age.

Endako Group

The Endako Group was the name given by Armstrong (1949, p. 74) toa
group of rocks along Endako River. These were described as “relatively flat-lying
lava flows, as much as 2,000 feet thick, that were erupted during Oligocene or
later time”. As mapped by Armstrong, the group extends with little or no break
into Nechako River map-area, where these or similar rocks can be traced without
a break to the south margin of the area. Although all these rocks mapped as
Endako Group are lithologically similar to the rocks of the type area and appear
to occupy a comparable stratigraphic position, there is no assurance that they
everywhere represent the same time span. The rocks along West Road River, for
instance, may be much younger than those north of Francois Lake.

The Endako Group within Nechako River area occupies the low parts of
the southeast half and fills pre-Miocene valleys in the hillier country in the north-
west quarter. Nowhere do rocks of this group occur above 5,000 feet elevation
and rarely above 4,000 feet. In the northwest quarter, near Cheslatta Lake, valleys
have been cut into the flat-lying flows to a depth of more than 2,000 feet, but in the
south half of the area dissection has not been pronounced and valleys over 300
feet deep in these flows are not common.

The group is best exposed along major valleys, where the eroded edges of the

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