Sawback Range (82O)
"After a halt for two hours during the most intense heat, we again started and crossed over a low point of rocks, close to the river, where we entered the second great valley, which is of magnificent proportions. Along the eastern side runs a wall of vertical beds, of light grey limestone, the serrated edges of which at once suggested the name of Sawback Range for them." -from James Hector's Journal -17 August, 1858.
The Sawback Range stretches for approximately thirty-five kilometres from the Bow Valley west of Banff to the headwaters of the Cascade River.
MAIN RANGES AND THE SAWBACK RANGE
Having had considerable training in geology, Dr. James Hector would undoubtedly have noticed the abrupt change in geology between Castle Mountain and the Sawback Range.
Geologists separate the Rocky Mountains of western Canada into four different zones which relate to the style and degree of their structural deformation. In the Foothills area the rock layers have been folded and faulted but not uplifted to a great extent. Farther west the Front Ranges appear, their eastern edge forming a very distinct boundary where older limestones have been exposed. These ranges are composed of a series of thrust faults that underlie panels of rock which overlap like the shingles on a roof. They are almost always tilted down to the west in varying amounts. To the west of the Front Ranges lie the Main Ranges of the Rockies in which the sedimentary layers remain relatively undisturbed although they have been uplifted significantly and moved eastward. Farther west, the layers of the Western Ranges are severely broken, faulted, and folded. The western boundary of the Rockies is the "Rocky Mountain Trench," a major valley filled with thick deposits of sands and gravels and containing major rivers such as the Columbia.
Castle Mountain is noteworthy because it is the eastern-most mountain of the Main Ranges in the Bow Valley. The rock is PreCambrian and Cambrian in age and the rock layers are relatively horizontal. The Castle Mountain Fault has thrust the older (400-600 million years) limestone which forms the cliffs and underlying older rocks over younger (200 million years) rock which has eroded and forms the tree-covered, gently sloped base of the peak. This fault defines the boundary between the Main Ranges and the Front Ranges and can be traced throughout Banff and into Jasper National Park where it passes between The Palisade and Pyramid Mountain, just east of Jasper Townsite.
Castle Mountain is, appropriately, a "castellate" type of mountain in which the flat-lying layers feature near vertical cliffs alternating with flat or gently sloped terraces which have been sculptured by glacial and other forms of erosion. The layers of rock involved vary in their resistance to erosion, the harder rock such as limestone being more resistant and softer rock such as shale eroding more easily. Castle Mountain demonstrates these principles with its two major cliffs of limestone being separated by a ledge which corresponds to a layer of shale.
While Castle Mountain is the easternmost of the Main Ranges, the Sawback Range, which was appropriately named by James Hector, is the westernmost of the Front Ranges. In this range the strata has been tilted to near vertical. "Sawtooth" type mountains have been formed as the steeply dipping, thin layers of sedimentary strata are eroded by cross gullies to form a series of inverted "V's' which resemble the teeth of a saw.