region around Lake Sullivan has come about as a result of several geologic
processes. In order from oldest to
- The oldest period of geologic history having a relevant effect
on the rocks, topography and the minerals found in the area is
the tropical marine environment the area enjoyed during the
Precambrian Eon and into the Early Cambrian Period (see
stratigraphic section below) of the
Phanerozoic Eon. This is when the North American Continent
rifted apart, creating a new coastline. The rocks that can be
used to prove the geologic setting are phyllites of the Maitlen
Formation (Alt, Hyndman, 1986). They date to around
Early Cambrian or around 540-500 MY ago. Within this formation
are phyllite rocks, which dominated the samples found at every
site we visited.
- During the Jurassic Period, the exotic terrane Quesnellia
(also called the Intermountain Terranes microcontinent) crashed
into the North American continent (Alt, Hyndman, 1995). Most
people don't realize that the coast of North America during
the Jurassic Period - yes, the same period that the dinosaurs
were roaming the lands and seas - was as far east as Idaho in
places. The site Spokane now occupies was then on a
westward-reaching portion of the continent.
- The crashing in of the Quesnellia terrane created an uplift
region in Washington and western Idaho called the Kootenay
Arc. This is a "belt of rock jammed hard into the former
western edge of the continent..." (Joseph, 1990). This "belt"
is highly deformed and contains many thrust
faults. This is the first of the uplifts that affected the
Lake Sullivan area.
- There were a several collisions from 570 to 100 million
years ago between the advancing North American continent
and a few subcontinents. The next major
accretion was the North Cascades subcontinent (Orr, Orr,
1996). The Insular Terrane is the succeeding terrane that
had an effect on the region.
- The collision with these exotic terranes caused not just
uplift but the continuous pressure resulting in folding
and faulting of the Earth's surface. This is how rolling
hills and most mountain ranges are made. This small
mountain range paved the way for glaciers to scour the
landscape when they came through.
- The third major event affecting the Lake Sullivan area was
the Pleistocene ice age continental
section of rocks in the Lake Sullivan area