Lava eruptions at least 140,000 years ago blocked the Bear River from draining into the Snake River system and forced it southward into what were then lakes Thatcher and Bonneville and is now the Great Salt Lake. From its source in the high Uinta Mountains of eastern Utah, the river doubles back on itself in a giant horseshoe shape, and this shift sent it south through the Grace area, where it carved a deep, rocky gorge in young basalt flows that complicated efforts to move irrigation water onto the surrounding fertile fields. The Last Chance Canal Company began in 1895 under pressure to meet an implementation deadline or lose water rights, and after years of perseverance, settlers finally got water to both sides of the Gem Valley in 1902. In 1916, Morrison-Knudsen Company was awarded the contract to create a tunnel through solid lava rock, ending years of trouble with wooden flumes along the river. Two brothers contracted by MK dug the canal from opposite ends of the rock barrier and met within a foot of alignment. Much of the drilling of the 1,800-foot tunnel, 12 feet wide and 9 feet high, was done with hand tools, and the rock was hauled out by a horse pulling a small rail car. At the tunnel outlet, workers built a new cross-river flume supported by a great concrete arch, while an upstream dam and headworks diverts water to the tunnel for irrigation and hydro-electricity generation. Built without federal assistance or outside capital, the project was carried out cooperatively by local farmers in the spirit of Mormon settlers. An all-steel flume replaced the concrete arch in 1946, but the arch remains as a reminder of the determined local effort that brought irrigation water to the Grace area, where much of Gem Valley farming and ranching would not exist without this project.