BACKGROUND - Canadian Rockies: Including Banff and Jasper National Parks - page 497

carrying the boulders with it. Many thousands of years later, as temperatures
warmed and the ice melted, the boulders were deposited far from their source, creat-
ing what geologists call an “erratics train”-a string of glacially deposited rocks that
in this case extends 650 kilometers (400 miles) south through Alberta. The largest of
these boulders-the world's largest erratic, weighing an estimated 18,000 tons-lies
just beyond the foothills, seven kilometers (4.3 miles) west of Okotoks. The name
is difficult to forget; it's called the Big Rock.
Waterways
Water in its various forms has had a profound effect on the appearance of the Canadian
Rockies. In addition to the scouring action of the glaciers, flowing water in rivers and
streams has, over the millennia, deeply etched the landscape. The process continues today.
The flow of water is directly related to divides, or high points of land that dictate the
direction of water flow. The dominant divide in the Canadian Rockies, and indeed North
America, is the Continental Divide. The natural boundary created by this divide forms the
Alberta-British Columbia border, while other, less obvious divides form borders of many
parks of the Canadian Rockies. The five national parks are classic examples of this scen-
ario. The divides forming the boundaries of Banff National Park encompass the entire up-
per watershed of the Bow River. The Bow flows southward through the park, then heads
east out of the mountains and into the Saskatchewan River system, whose waters continue
east to Hudson Bay and the Atlantic Ocean. The Bow River is fed by many lakes famed for
their beauty, including the Bow, Louise, and Moraine. To the south, the rivers of Kana-
naskis Country and Waterton Lakes National Park also drain into the Saskatchewan River
system.
The boundary between Jasper and Banff National Parks is an important north-south di-
vide. The Columbia Icefield, a remnant of the last ice age, lies on either side of this di-
vide. Runoff from the south side of the ice field flows south into the Saskatchewan River
system, while runoff from the north side forms the upper headwaters of the Athabasca
River system. The Athabasca flows north through Jasper National Park and into the Mack-
enzie River system, which continues north to the Arctic Ocean. All water draining off
the western slopes of the Continental Divide ends up in the Pacific Ocean via two major
river systems: the Columbia and the Fraser. The mighty Columbia makes a wide northern
loop before heading south into the U.S. state of Washington and draining into the Pacific