111

CHAPTER IV
STRUCTURAL GEOLOGY
GENERAL STATEMENT

Folds and faults of variable intensity have disturbed the strata in the
several physiographic regions of northeastern British Columbia. On the
Plains, late Lower and Upper Cretaceous terrains are gently sloping or flat
lying or, near their western margins, are gently folded. In the Foothills,
Triassic, Jurassic, and early Lower Cretaceous strata are disturbed by open
folds and faults. In the Rocky Mountains, as yet little studied, Proterozoic,
Paleozoic, and in places Triassic, formations have been subjected to over-
thrust faulting and some folding. At the southern end of the Liard Plateau,
late Paleozoic, Mesozoic, and Paleocene beds are folded and faulted. In
the Rocky Mountain Trench, late Cretaceous or early Tertiary beds are
folded and may be downfaulted. In the Cordillera, west of the Trench, late
Proterozoic, Paleozoic, and Mesozoic strata, including both volcanic and
sedimentary rocks, are intensely folded and faulted on a large scale, and
are intruded by igneous bodies of batholithic dimensions.

The regional structural trend in the Rocky Mountains and Foothills
of northeastern British Columbia varies, but averages about north 20 to
30 degrees west. The direction of the Trench is about north 30 degrees
west, so that the folded and faulted belt between the Trench and the Plains
widens from southeast to northwest.

In some parts of the region the structures of the Foothills decrease in
intensity so uniformly and pass so gradually into those of the Plains that
it is difficult, on a structural basis, to know where to draw a boundary.
Even where this can be determined, it has been found convenient, in
describing some sections, to include structures on the Plains along with
those of the Foothills; otherwise some that are closely connected would be
isolated from one another in the text.

The structures of the Foothills have been more carefully and intensively
studied than those of other physiographic divisions of the region, and more
has been published concerning them.

INTERIOR PLAINS
PINE AND PEACE RIVER VALLEYS

The structure of the Plains in the vicinity of Pine and Peace River
Valleys has been studied by Gwillim, Spieker, Dresser, Williams, Bocock,
Stelck, and others. Although valuable work has been done, the structural
study of this area is not complete. Moreover, most of the recent investiga-
tions have been recorded only in manuscript, which, not having been
prepared for publication, can only be quoted with reserve. Some anticlinal
axes between Moberly Lake and Kiskatinaw River and between Hudson