Sorry folks, it's just a gardening tool. Move on, nothing to drink here.
A San Angelo bar is a 5-6 foot long, inch-think bar of steel. It has a chisel-like head on one end, and (usually) a flat disk welded to the other end. They weigh about 14-18 pounds, and are closely related to the rock bar. One uses a San Angelo bar to dig though hard, rocky, or frozen soil. You use the chisel end to break up the dirt, and the flat disk (usually about 3 inches in diameter) to tamp dirt back down when you're done. They are used for digging post holes and ditches, clearing out roots, and prying out rocks.
There is also a variation known as the Pencil Point San Angelo Bar, where the tamp disc it replaced with a thin rounded spike.
AKA a spud bar (because of its sharpened end), or tamper bar (because you use it to tamp). I have not been able to find any information on why they might be called a San Angelo bar (perhaps they were invented there), but this is the name that they are marketed under by those few companies that make them.
San Angelo bars are dead useful, whether trying to remove rocks from your yard, digging in hard soil, or fighting off the zombies. They are the largest digging bar that most hardware and gardening stores carry, and while they are not quite as heavy as some rock bars, they can do most rock-prising jobs.
Transitional Man reports that roofers in his area use these and call them spud bars. A quick Google search confirms that in the roofing and construction industries these are more likely to be called 'spud bars' than 'San Angelo bars'. Overall, the term San Angelo bar appears more often than spud bar, implying that this tool more used by gardeners than contractors.