A great dam of glacial ice once blocked the northward passage of the rivers that form Coeur d'Alene Lake and towered above the horizon as far as the eye could see. When the glacier melted about 600,000 years ago, it left a moraine, a ridge of rubble gathered under the glacier front, at Rathdrum, Idaho, northwest of here. This moraine dammed the rivers, and run-off waters were forced west to form what is now the Spokane River. Coeur d'Alene Lake has an area of 50 square miles, a length of 32 miles, an unknown depth, and an elevation of 2,124 feet.