(This is an excerpt from All that was Promised by Blaine M. Yorgason.
Now came the challenge of preparing footings in those boggy areas that would be firm enough to support the temple’s foundation.
According to Charlie Walker, Brigham Young also identified the solution to that problem. As he delivered an address in St. George on 15 February 1873, the prophet “spoke of the building of the Temple and the manner of making the foundation, by putting in small volcanic rocks and driving them down with a pile-driver.” Immediately this plan was put into operation as the youth, followed by almost everyone else in town, began gathering chunks of volcanic lava, both large and small, carrying them to the deep excavation and dumping them in...
Day after day wagonloads of lava stones and rubble were hauled from the Black Ridge and the other lava-topped ridge to the east (called Foremaster Ridge today) and dumped into the massive excavation; so too were dumped bags-full, baskets-full, aprons-full, and every other available container filled with chunks of lava that young and old alike were busy gathering from wherever they happened to be. Gradually the piles of rubble in the bottom of the excavation grew, the ultimate goal being to form a rock-solid footing upon which the temple’s foundation could be built.
But how to pound these thousands upon thousands of stones into the seemingly bottomless mud until they formed that footing? And where to find a pile driver such as Brigham had suggested? That would be no simple task. But then someone remembered the cast iron cannon owned by the town militia. Its barrel was filled with lead, encased with thick oak staves held in place by iron bands that were pounded into shape and secured tightly by Samuel L. Adams and other local blacksmiths, and its butt end was used as the pile driver! Thus was created a pile driver weighing between 800 and 1,000 pounds.
But the next problem was how to hoist the pile driver high enough, trip it, and allow it to free-fall onto the stones below. The original Salt Lake and St. George plowman, William Carter, came up with the answer.
He devised a 35-foot-tall movable derrick of thick timbers with a system of pulleys at the top that, with a jerk on the rope from one of the men below, tripped the cannon and allowed it to fall freely, even though the chains or ropes running through the pulleys remained connected to the cannon. To make that connection, Carter bolted two iron rings into the wooden staves at the muzzle end of the cannon and hooked them to the ropes running through the pulleys. Mules towed the main rope or chain, hoisting the cannon 30 feet into the air. There it was tripped, and it fell, its crushing weight driving into the mud whatever rock it was aimed to hit.
Because the widest end of the cannon pile driver was little more than a foot across, this tedious process had to be repeated over and over again, day after day, thousands upon thousands of times. Only in that manner could the untold tons of fragmented lava rock be pounded into the boggy excavation to form a solid footing. Brigham Young had told them they would know when it was ready for the foundation stones only when the cannon, “when dropped, bounced three times before coming to rest.”
All That Was Promised, Blaine M. Yorgason, pp. 99-103.