Once I heard the story, I just had to see the spot myself. It was too good to be true.
The Swasey Brothers settled on the Swell country in the 1870's, when is was a country of horse thieves, rustlers, outlaws, and bad men in general. They were a rough bunch in a rough largely unsettled unexplored country, known only by roving Indian bands, a few solitary trappers, and the ranchers who managed to brave the harsh weather and unfriendly environment to get lucky with a few bony rangy tough cows.
The Swasey Brothers lived as tough as their livestock. Sid once made a bet with his brother for a herd of livestock that he could jump his horse across the San Rafael River -- a modest jump of some less than than 20 feet or so. But it was spanning a horrendous chasm above the river at a dizzying height. Any slip or miscalculation would certainly plunge horse and rider to sure death in the canyon below.
Sid closed the bet, and rallied his horse for the jump, with no thought of the fearful consequence for a near-miss. They plunged forward and leaped, and sailed across the canyon.
Dust showered down the sides as they crossed through space, but the horses feet planted firmly on the other side. He made it! History doesn't say whether it was by an inch or a foot, but his brother gladly paid up on the bet.
Swasey's Leap is on the other side of the Lower Black Box. Look for trail maps if you want to visit there. It is a long 4wd trek, and the trail is obscure, best use GPS and topo to be sure. Don't try to down-climb without rappelling gear and experience. This is serious rock!
(I did some solo unroped climbing here and other places. Very stupid, not recommended, unless you are seeking suicide-class thrills.)