In the spring of 1926, when the water of the Burlingame Irrigation Ditch was diverted for one week into a diversion channel, a miniature Grand Canyon, in places 100 feet wide and 100 feet deep, was created; thousands of tons of silt were carried to the Columbia. In the walls of this gully, the stratified deposits of an ancient lake bed may be advantageously studied. Deep-well drilling in artesian basins has revealed that this region was occupied in succession by four lakes. That the earliest antedated the uplift of the Cascades is shown by the blue clay deposits characteristic of the pre-Cascadian period, and characteristic granite boulders indicate that the last lake existed in the Glacial period.