As Minneapolis (and its former neighbor across the river, St. Anthony) developed, the water power at the falls became a source of power for several industries. Water power was used by sawmills, textile mills, and flour mills. Millers on the Minneapolis side formed a consortium to extract power by diverting upper-level water into waterwheel-equipped vertical shafts (driven through the limestone bedrock into the soft, underlying sandstone) and then through horizontal tunnels to the falls' lower level. These shafts and tunnels weakened the limestone and its sandstone foundation, accelerating the falls' upriver erosion to per year between 1857 and 1868. The falls quickly approached the edge of their limestone cap; once the limestone had completely eroded away, the falls would degenerate into sandstone rapids unsuitable for waterpower. The mills on the St. Anthony (east) side of the river were less-well organized harnessing the power, and therefore industry developed at a slower pace on that side.