Calgary's location at the confluence of the Bow and Elbow Rivers provides an adequate water supply. Moreover, the proximity of the Rocky Mountain foothills and the wooded eastern slopes of the Rockies supplies wood for fuel and building an asset not enjoyed by locations further east on the plains. Using logs floated down the Bow River, lumber mills were amongst the earliest commercial endeavours in Calgary Proximity to the mountains also accounts for the region's distinctive climate. The prevailing westerly winds, called Chinooks, that descend the eastern slopes of the Rocky Mountains are dry and warm and cause vast temperature fluctuations, especially in the winter where in the short space of a few hours the temperature can climb from well below freezing to 8-10C. As a result, the hillsides are often bare for much of the winter, making the foothill country to the west and south a prime stock-raising area. Calgary's commercial advantage had resulted, in large part, from its proximity to one of the very few passes through the mountains suitable for rail and road traffic.
