IT'S A FIERY JUNE MORNING at Grapevine Camp, a spit of sand tucked along the banks of the Colorado River, deep inside the stone walls that frame the sub-basement of the Grand Canyon. From the surface of the river, the walls soar upward for more than a vertical mile, exposing geology that extends 17 million centuries into the past. During that span, the oceans have swollen and receded a dozen times, the continents have slammed together and cracked apart again, and a chain of mountains higher than the Rockies has been heaved into the sky and reduced to gravel.

Philosophically speaking, this is some heavy shit. Heavy enough to make a man perched on the bow of a humble raft at the edge of Grapevine—a man now staring at that staggering immensity of stone—scratch his head and wonder what it all might suggest about his own place in the universe.

But that doesn't last long. Any confusion about where I fit into the cosmos is vaporized by the arrival of a hefty steel box that two of the guides on this 19-day river trip are slinging onto the aluminum deck of my raft with a rude, clattering ka-thunk.

"Heads up, there, my friend," warns Bill "Bronco" Bruchak, a boatman who's built like the beer truck he used to drive in Pennsylvania. "Don't pull a muscle when you lift this thing."

"Yep," chimes in Mike "Milty" Davis, a small, cheerful guy with mischievous eyes and a snowy white beard. "That is one enormous box of poop."

I seize the handles, heft the cargo, and stagger toward the tight space between the stanchions that cradle my 12-foot-long, fiberglass-reinforced oars. Two identical canisters are already anchored on both sides of the footwell, which is where I sit when I row this barge. The top of each can is emblazoned with a strip of red electrical tape labeled FULL!!!

As I start lashing down the new can, I glance over at Monte Tillinghast, who's piloting the second baggage boat on this trip, a kitchen raft that's tied up next to mine.