120

structural features of the Peace River Foothills are narrow zones of anti-
clinal folds commonly broken by high-angle thrust faults, separated by
broad synclinal basins of gently folded strata” (Beach and Spivak, 1944).
Mathews (1947) has made similar statements.

Another feature of the structure in the Peace and Pine River Foothills
is the ‘flat-topped’ or ‘box’ anticline (Beach and Spivak, 1944; Mathews,
1947). Thus, on some anticlines, the dip near the crest is low and on the
flanks is high. The same authors note that on such anticlines much of the
folding is concentric rather than similar, and Beach and Spivak infer that
“such folds are more superficial than folds of similar size in the southern
Foothills”’.

HALFWAY RIVER TO PROPHET RIVER

Pink Mountain Structure
(See Figure 3)

Although it is difficult, on a structural basis, to draw a line between
Foothills and Plains in the area extending from the Halfway to Prophet
River, the Pink Mountain can without doubt be included among the Foot-
hills structures. It has been described by Hage (1944).

On Pink Mountain the Triassic Pardonet beds, the Jurassic Fernie
group, and the Jurassic? and Lower Cretaceous Bullhead beds are folded
into a long, narrow anticline, with a southwest-dipping thrust fault on the
northeast limb. The crest of the fold is broad and low-dipping and the
“limbs have dips averaging from 50 to 60 degrees. Some of the beds
along the northeast limb north of Halfway River are overturned”. The
south closure is about 500 feet and the north closure near the Gap is more
than 1,000 feet (Hage, 1944).

Halfway River Valley

The structure along Halfway River, west of Pink Moutain, has been
little studied, but a few folds have been noted. About 5 miles west of
Quarter Creek, the ‘Grey beds’ are folded into an anticline. Still farther
west, the axis of a syncline in the Bullhead group centres on Grave Creek.
The beds of this group outcrop and rise to the southwest on the southwest
limb of the Grave Creek syncline and northeast limb of an anticline, the
crest of which is on Grave Ridge. Other folds were noted in the high hills
west of Grave Ridge. East of Grave Creek, beds of the Bullhead rise on
the southwest limb of an anticline that exposes Triassic beds on hills east
of this Creek.

Farther west, Triassic formations are nearly flat at the east end of
Mount Wright in the Fourth Gully (See Plate III B). Triassic ‘Dark,
siltstones’, ‘Grey beds’, Pardonet beds, Jurassic Fernie shales, and Jur-
assic? and Lower Cretaceous Bullhead strata dip at a high angle at the
west end of this mountain.

Structures in Sikanni Chief Valley
(See Figure 3)

The section on Sikanni Chief River has been described by Hage
(1944). The cross-section plotted by him extends from the Alaska High-
way nearly, but not quite, to the Rocky Mountain front.