The stench of death hung heavily over Gibson Ranch Regional Park on Saturday.
Or maybe it was the odor of sweaty socks and muddy running shoes.
About 5,000 runners took part in the Running Dead Zombie Mud Run, scaling obstacles and working their way through mud pits.
And as if that weren't enough to add some spice to the 5-kilometer course, 100 zombies were unleashed on the trails, tasked with trying to rip flags from the runners in a series of symbolic body-snatchings. As a result, it was not unusual to see one runner using another as a body shield.
"They yell like we're coming to eat them," said Maricela Cisneros, a volunteer zombie dressed in a mangled wedding gown. She and her boyfriend, Sam Lizarde, were stationed about 200 yards from the finish line and spent a good part of the morning picking off exhausted runners limping down the final stretch.
The event combined two fads gaining in popularity: mud runs and zombies.
Mud runs like the Tough Mudder series have attracted thousands of runners to the world of obstacle-course racing. Zombies have had a resurgence, led by the critically acclaimed AMC television series "The Walking Dead."
The race scene had many elements of your typical Saturday fun run. Most of the runners seemed at least somewhat athletic, and there was a guy dressed like Elvis just as there is at so many other races.
Any doubt that this event was typical, however, evaporated quickly.
At one point, an announcer urged runners to not "harass the zombies" (apparently one or two had been punched). There also seemed to be an exorbitant number of runners dressed in tutus.
For avid runners like Brian Wedel, Chuck Rucker and Marc Krichman none of whom was wearing a tutu, by the way being chased around by a bunch of zombies presented a new challenge. All three got into the spirit by decorating their faces and necks with fake blood. Though they compete in several road races a year, each said the zombie mud run was an unexpectedly decent workout.
"You get lulled into a sense of security and then all of a sudden you're surrounded," said Wedel.
"They were athletic," Rucker said of the zombies.
Well, not all of them.
A few hours before they were scheduled to head out onto the course, A.J. Buckeye, Bre Corum and Pedro Martinez were going over the final touches on their zombie gear with one hand and sipping cans of beer with the other.
"I've done a couple of 5Ks and to me, that may as well be a marathon," Corum said.
"They want us to be sub-athletic," bragged Buckeye.
The group along with some other friends was up all night getting ready. Their makeup was a mixture of gelatin, glue and toilet paper, along with a pretty healthy dose of fake blood.
"We're zombies at heart," said Corum.
The event was the brainchild of race organizer Dustin Ryen, whose background is in concert promotion. He said he liked the idea of a mud run because such a race is accessible "to a wide variety of fitness levels."
As for the inclusion of zombies, Ryen said he and his wife are big fans of "The Walking Dead."
His passions are apparently shared by others. There's actually another zombie run next weekend in Sacramento's Miller Park and a similar race was held Saturday in Temecula.
"People feed into it like it could actually happen," Cisneros said of a post-apocalyptic world ruled by zombies. "Getting eaten alive is what freaks people out."