The Black Box. Shortly after Buckhorn Wash joins up with the San Rafael River, the canyon empties into a broad, scrub-covered flat. Geologically, the flat region is the top of the Kaibab limestone, a relatively hard rock layer that has resisted erosion, while the younger sandstones above it have been completely washed or blown away. Though it's relatively flat, the land continues to rise towards the southeast, forcing the river to cut a second canyon into the dolomitic limestone.

The open flat was the most deserted place we went on the entire trip. We drove there about mid-day, with temperatures somewhere in the mid-90's. After bouncing down a dirt track for 15 miles or so, we came to a stop in the middle of what appeared to be an open valley, rimmed by cliffs to the north, east, and west. The day was cloudless, windless, and apart from whatever noise our little party made, soundless. Up at the wedge, we had run into two other people; in Buckhorn Wash, a rather inquisitive sheriff stopped to chat; but out here there was no one, and based on the lack of tracks there hadn't been anyone for at least a week. Definitely the sort of place something bad could happen to you and nobody would notice for a long time.

After a strictly utilitarian lunch, we hiked southeast through the rocks and scrub, and came to the edge of the Black Box. The Black Box is the slot canyon that the San Rafael has cut through the dolomite into the Coconino sandstone beneath – the oldest rock exposed in the Swell. The rock here is so hard that, aside from the cutting action of the river itself, it has been only slightly eroded, and so the canyon is basically only as wide as the river is.

This was the only place we went on the whole trip where I thought, whoa, that's scary. It's a long way down, and it's straight down. Because there's no clear cliff edge, it's tempting (especially for adolescents) to get just a little closer... a little more...

It's a frustrating thing to try to get a picture of, because it is very hard to give a sense of scale. (Yes, I know, putting actual people into the pictures might help, but we're vampires and don't show up in photos.) I don't know the canyon width, but our empirical testing showed that a 13-year old boy could easily throw a golfball-sized rock well onto the other side of the canyon.
Further tests (conducted after waiting to see if anyone was floating down the river) were conducted to determine depth;
[rock tossed over side]
one second...
two...
three...
four...
five...
BOOM!
The echo was startlingly loud. Let's see: distance = 9.8 * time² / 2... about 122 meters, or about 400 feet down. (That more or less agrees with the topo map, which gives depths of about 400 to 600 feet for this part of the canyon.)

To give you some idea of scale, those green shrubby things on the far side of the canyon are junipers, about 15 feet tall.

Shortly downstream from here, the rock drops down to near river level and the canyon opens up. The river makes a hairpin turn and re-enters the hard limestone, creating a second slot canyon, the Lower Black Box. A spot on the Lower Black Box is known as Swazy's Leap, after an early settler who allegedly bet a herd of sheep that he could jump the canyon on his horse. (He could.)

(An uncropped version of this photo here.)

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Posted by David Fleck at 22 September 2006 07:22 AM