Here's how widespread the bad smell was Monday: When Aubrey Farkas heard people saying the source of it might be the Salton Sea, she said, "I don't even know where that is."

No surprise, perhaps -- the nearest part of the Salton Sea is about 160 miles from her office in Sherman Oaks.

Beginning early Monday, scores of people reported a rotten egg odor to fire departments or air quality officials, and likely thousands more smelled it -- if not millions.

In addition to swaths of L.A. County, it was reported in Ventura County to the west and San Bernardino and Riverside counties to the east.

Even a few people in Orange County smelled it.

On one online map, readers reported the smell as far as Simi Valley to the west, Temecula to the south and close to Lancaster to the north.

No one using the freeways could possibly have traveled so far so fast in Southern California.

Monday evening, officials said they weren't sure of the cause, but "several factors" pointed toward the Salton Sea.

The South Coast Air Quality Management District, an intergovernmental body that regulates air quality in much of Southern California, sent field inspectors to the San Fernando Valley, Long Beach, Colton, San Bernardino, Riverside, Perris, Temecula, Banning, Palm Springs, La Quinta and the Salton Sea on Monday.

In a press release, Barry Wallerstein, executive officer of the district, said it's unusual for odors to remain so strong 150 or more miles from their source, but thunderstorms around the Salton Sea and high winds from the southeast apparently pushed air toward Los Angeles.

A highly saline body of water spanning Riverside and Imperial counties, the Salton Sea is infamous for its smell thanks to massive fish die-offs.

Brentwood, below, Century City, center, and downtown Los Angeles sit under a blanket of smog in this file photo from Jan. 14, 2000.
Brentwood, below, Century City, center, and downtown Los Angeles sit under a blanket of smog in this file photo from Jan. 14, 2000. (AP Photo/Mark J. Terrill)

Andrew Schlange, interim general manager of the Salton Sea Authority, said gases likely built up from decayed bacteria after a recent fish die-off.

Brian Humphrey, a Los Angeles Fire Department spokesman, said dozens of people reported the smell in L.A., mostly in the Foothill area and the northern San Fernando Valley.

Cue the inevitable jokes.

"#SmellsliketheValley" went one Twitter hashtag from someone who goes by @LAScanner.

Even before any official word on the cause, people ventured guesses, educated or not. Regional stereotypes came into play -- and not just in the Valley.

Roberta Marroqui of Rancho Cucamonga said, "It smells awful. You know what, I think it's the cows from Chino."

Most people described the smell as like rotten eggs or sulphur.

Farkas had a more specific description for what she smelled while getting coffee in Studio City before work: "ketchup and eggs."

It was a childhood flashback for her -- though not a pleasant one.

"I don't really like ketchup with my eggs," she said.

The smell led to some oddly poetic comparisons.

"Why does the entire valley smell like ocean chum today?" wrote @lacantdrive on Twitter.

John Bradford, a 69-year-old in the San Bernardino County city of Rialto, had no complaints about the air but said his tap water tasted like "dirty socks and underwear."

In Chatsworth, Arlet Abrahamian opened the door to her garage and wondered, "Did something die in here?"

The smell seemed to dissipate in the afternoon. It wasn't apparent in Granada Hills or Chatsworth after lunch, and Farkas said it had gotten weaker in Sherman Oaks.

There were people who smelled nothing all day. Writing online, some of them were happy to have missed out, while others seemed almost jealous of those who had experienced the smell.

Ana Jones of L.A. wrote on Twitter she didn't smell anything, perhaps because she had a cold.

Her conclusion: "WIN!"

Josh Dulaney of The San Bernardino Sun contributed to this report.