The values of the event are simple: Mud is honorable; the more mud, the more honor.
Living up to those values is a challenge.
Two weekends each year, thousands of civilians flock to this sprawling base for a chance to get muddy and exhausted in the World Famous Mud Run.
Some are weekend athletes striving for a personal best on either the 5K or 10K course. Some are members of teams from their workplaces, churches, schools or neighborhoods.
"Who doesn't love mud?" said Margie Carroll, 44, of the team from the Kleinfelder engineering/architectural/science consulting firm.
With that ethos Saturday, Carroll and an estimated 5,000 other participants ran, crawled, jumped, struggled, slithered and dog-paddled around courses with slippery hills, a tunnel crawl, a cargo-net climb, a 30-foot mud pit, tire obstacles and more.
By the end of next weekend, an estimated 20,000 mudders will have challenged the courses. The money raised will go toward programs for Marine families.
There are other mud events throughout the region. But the one at Camp Pendleton offers something not available anywhere else — or at least that's the come-on.
"This is high-caliber mud, you can't get this at your spa!" shouted the starter just seconds before setting off the first wave of runners. "This is Marine Corps mud!"
After finishing the course, mud-caked runners were directed to outdoor showers where Marines with bullhorns provided motivation: "Hurry up, hurry up, hurry up, get out of my shower!"
Some team shirts were emblazoned with in-your-face messages: "Hot Beasts," "On the 8th Day God Created Tankers and All Hell Came to Attention," "I Prefer Muddin' Over Runnin'" and "Never Give Up, Never Surrender, No Mercy."
The 300 Spartans team runs every weekend. Next week: a mud run in Monterey.
"Anything with mud in it, we're there," said Dennis Skibinski, 42, a former Navy rescue swimmer. "Our motto is 'Live free, eat dirt.'"
There were runners dedicated to honoring others.
A group from Children's Hospital in Los Angeles was called Team Louis after a nurse with health issues (he's getting well, they said). A team from the Los Angeles Police Department was here to honor fallen colleagues, including Officer Nicholas Lee, killed March 7 in a traffic collision.
Family members of Marine Lance Cpl. Evenor Christopher Herrera, who was killed in Iraq in 2005, assembled from Las Vegas, Orange County and Los Angeles to make the run. All wore T-shirts in Marine red and with "Herrera 05" on the back.
Though there has never been a disruptive incident at the World Famous Mud Run, security has increased in the wake of the Boston Marathon bombing. Marines with M-16s strolled through the crowd.
As mud running has increased in popularity, the Camp Pendleton event has evolved and now includes an outdoor rock concert, carnival rides and food vendors. Big Bubba's Bad BBQ was doing particularly brisk business.
On the concert stage, the Southern country/rock band Austin Law sang the praises of Norco, Calif., where horses roam and the streets are painted red, white and blue. "I'm glad to be from an American town," sang resident Michael Austin.
It's not quite 50-50 yet, but the number of female mudders is increasing. Among them: a group of mothers with children at St. Edward the Confessor Parish School in Orange County.
The women were mudding while the men stayed home with the children. "This is Mom's day out," said Melissa Lapena, 47.
For civilians, the mud run is a chance to get a look at Camp Pendleton, a 120,000-acre gated community not usually open to visitors. For Marines, it's a chance to show civilians what they do.
Some mud-splattered runners gathered for selfies with Marines or in front of a large American flag. Others asked about the howitzers parked just outside the fun-and-food zone. And still others tried on the blast-protective gear worn by explosive ordnance disposal specialists.
"It's good that they know our capability," said Staff Sgt. Steven Cauley, 30, who has deployed to Iraq and Afghanistan with EOD units.