As the name implies, the Mud Run pits contestants against a 6.2-mile course dotted with obstacles, most of which involve mud.
"I just hope they can medevac me out," runner Greg Copeland, 60, Irvine, told the Los Angeles Times at the starting line.
The Times said the Mud Run began in the 1990s as a modest event in an area where foot races ranging from marathons on down take place nearly every weekend. This year, the Mud Run was stretched across two days to accommodate its growing popularity.
Navy Corpsmen treated various cases of strains bruises and heat exhaustion while Marines stationed along the course bellowed out encouragement not to quit.
The reward was self-satisfaction and camaraderie among the filthy finishers. "When you're done and hot and muddy, we've got ice-cold beer and hot barbecue," said base commander Col. Nick Marano.