Blocked by lava eruptions at least 140,000 years ago, the Bear River was diverted from draining into the Snake River system.
It was forced to drain southward into what were then lakes Thatcher and Bonneville and is now the Great Salt Lake.
The river direction doubles back on itself from its source in the high Uinta Mountains of eastern Utah, forming a giant horseshoe shape.
The shift sent the Bear River south through the Grace area, carving a deep and rocky gorge in young basalt flows.
The gorge complicated any effort to move irritation water onto the surrounding fertile fields.
The Last Chance Canal Company, a name that described the settlers' desperation, began in 1895.
They had an implementation deadline to meet or lose their water rights.
The early pioneers persevered, and their ingenuity finally got water to both sides of the Gem Valley in 1902.
Morrison-Knudsen Company (MK) was awarded the contract in 1916 to create a tunnel through solid lava rock, solving years of trouble with wooden flumes along the river.
Two brothers, contracted by MK, dug the canal.
They began at 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.
The rock was hauled out with a horse pulling a small
At the tunnel outlet, a new cross-river flume was constructed and supported by a great concrete arch. An upstream dam and headworks diverts water to the tunnel for irrigation and hydro-electricity generation. The engineering masterpiece was built without federal assistance and without outside capital by local farmers who worked cooperatively in best spirit of Mormon settlers.
An all-steel flume replaced the concrete arch in 1946. The arch remains, a reminder of the determined local efforts that brought irrigation water to the Grace area.
Much of Gem Valley farming and ranching would not exist without this project.