When Halloween arrives on Oct. 31, it will feel like a grand finale, the culmination of a multi-month celebration of events around Southern California.

Spending for Halloween is estimated to be at some of its highest levels in history, and social media has had a multi-year obsession with giant skeletons and now a talking pumpkin named Lewis. But much of the modern culture surrounding Halloween can arguably be traced back to Southern California’s theme parks.

One can make the case that the unofficial first day of Halloween this year was Sept. 1, for that was the day Disneyland Park opened its overlay of the Haunted Mansion themed to Tim Burton’s “The Nightmare Before Christmas.” And Southern California is home, after all, to one of the longest-running large-scale Halloween events in the county, the month and a half-long makeover of Knott’s Berry Farm into Knott’s Scary Farm, now in its 50th year.

Americans have become Halloween-obsessed. By the time Nov. 1 first rolls around, it’s estimated that we’ll collectively have spent a record of more than $12.2 billion to celebrate Halloween this year, up almost $2 billion from last year, according to the National Retail Federation. And in a testament to how theme parks can shape and drive culture, we have them partly to thank — or blame.

“I wouldn’t even say partly. I would say gigantically,” says Lisa Morton, who has written multiple books on the holiday, including “Trick or Treat: A History of Halloween.”

Disneyland is part tourist attraction, part cultural institution, and our country’s gradually changing view of Halloween — one from a costume-and-candy-driven day of partying to nearly two months of horror or spooky-themed extravaganzas — is evident in how the Anaheim institution has evolved from once barely acknowledging the holiday to being completely consumed by it. With a sold-out separately ticketed evening party called the Oogie Boogie Bash and decorations and ride makeovers across two parks, Halloween at Disneyland rivals — and in some cases exceeds — the Christmas season.

“I would venture to say it’s more popular because there’s typically more days,” says Charlie Price, who works in animation with the Walt Disney Co. and is a co-author of the coffee table-style book “Holiday Magic at the Disney Parks: Celebrations Around the World from Fall to Winter.” Price points to Florida’s Walt Disney World, where that resort’s Halloween party in the Magic Kingdom — Mickey’s Not-So-Scary Halloween Party — begins even earlier than its Southern California counterpart in mid-August. “They start in August because there is such a demand for it.”

While Disneyland does not release attendance information, there’s at least some evidence that the Halloween season does indeed rival Christmas in terms of guest popularity. In data compiled by travel site Touring Plans, which monitors wait times at the Disney theme parks, last October saw higher average wait times than in November and December, but not by much more than a minute or two.

It wasn’t always the case.

There’s evidence of Disneyland embracing Halloween all the way back to the ‘50s. In Walt Disney’s era, the park advertised itself via participating in Anaheim’s long-standing fall festival and Halloween parade, now in its 100th year. Yet Halloween was primarily celebrated in fits and starts by the park. One of Disneyland’s first major Halloween events occurred in 1959 with a parade of pumpkins, in which Disneyland gave away 1,000 pumpkins to be carved or dressed up for a contest.

But even if Disneyland wasn’t going all-in on Halloween, it was still driving the culture surrounding it. Morton cites a couple key moments in American pop art that were pivotal in shaping and leading to our modern era in which Halloween stretches long before Oct. 31.

“Knott’s Scary Farm and the Haunted Mansion at Disneyland, both ... got started within a few years of one another,” Morton says. “Haunted Mansion opened at Disneyland in 1969, and Knott’s did their first Halloween event in 1973. You see a lot of modern-day professional haunters pointing especially to the Haunted Mansion as a huge influence.”

Local event organizers who are known for specializing in the macabre give theme parks props for fueling the industry. Take, for instance, JFI Productions’ “The Willows,” a highly interactive immersive theater show set in a mansion on the outskirts of Koreatown in which guests are wined and dined while they uncover a twisted family history. “The Willows” just extended its run this year into November. While darker and more sinister than the Haunted Mansion, wandering the massive house with hidden nooks and weird personalities is reminiscent of the ride.

“Theme parks are the pioneers. It’s where every inspiration came from,” says JFI founder Justin Fix. “I don’t think there’s any author who can [criticize] Universal’s Halloween Horror Nights or Knott’s Scary Farm because they were the pioneers in this. I think our audiences are getting smarter, and I think our audiences want more.”

Disneyland, Price says, would be awakened to just how hungry audiences were for Halloween events in the mid-90s.

“It hit them by accident,” Price says. “They didn’t want to be Knott’s Scary Farm or a Halloween Horror Nights. That wasn’t what they were going for. So they were trying to figure out what they could do. And it all changed 29 years ago. It was Oct. 31, 1994.”

That is when Disneyland staged what ultimately became a misguided promotion in partnership with KIIS-FM. It was announced that Disneyland would give free admission to anyone who arrived in costume prior to 8:30 a.m. on a Monday. Guests started descending upon the park at 5 a.m., Anaheim streets became gridlocked and an estimated 50,000 showed up before the 8:30 a.m. cutoff time. Disneyland shut its gates and turned away guests.

The Times reported that those dressed as “ghouls, witches and machete-toting murderers gathered at the Haunted Mansion.” A Disneyland public relations representative said at the time: “We’ve never really done anything. We decided if we were going to do something, it should be pretty big.”

Price says, “It was so unexpected with the amount of attention that it got. They realized, ‘Hey, we’re onto something.’ They were at capacity at 8:30 in morning.” Even at its busiest, it’s incredibly rare for Disneyland to reach capacity when gates open. Disneyland, Price says, knew then that it had to capitalize on Halloween.

There had been an operational reason the park had hesitated to fully champion Halloween until then. Before the holiday became the high-trafficked Disneyland season it is today, the park would use the fall to do attraction maintenance before the Christmas season, Price says.

In 1995 Disneyland would stage its first large Halloween party. At that time, Disneyland still seemed unsure of just how badly guests wanted to observe the holiday. Decorations for its first experiments with nighttime, ticketed events were removed after each party, and the events did not occur every year. It’s a far cry from today. Main Street, U.S.A. is now a consistent explosion of autumnal colors and pumpkin oddities — a guest favorite is the Elvis pumpkin that adorns the music shop.

Halloween decorations became a staple in the early 2000s and by the mid-2000s, the park fully committed to yearly Halloween parties. “They realized the guests really enjoy this,” Price says.

At that time, Disneyland was gradually finding its Halloween footing but also still searching for an identity to anchor its season and events around. Among the cultural touchstones that Morton cites as influencing how America celebrates Halloween were two films, one of which was a Disney property.

“There are very specific happenings,” Morton says. “I point to the release of John Carpenter’s ‘Halloween’ in 1978 as one of the key things that transformed Halloween into an adult holiday. There had been nothing like that before that painted Halloween in a very frightening way. Counterculture movements were claiming the holiday more and more in the ‘70s, and that all cemented Halloween into an adult holiday. And then in the ‘90s you get ‘The Nightmare Before Christmas,’ and that restores the more whimsical side of Halloween.”

The sustained popularity of “The Nightmare Before Christmas” would gradually remake the tone of the Disneyland Resort’s Halloween events. Early Disney California Adventure Halloween offerings, for instance, included the lighthearted Candy Corn Acres, a farm of oversized candy corn. Today the park’s entrance is graced with Oogie Boogie, the villain from “The Nightmare Before Christmas,” and its center features a Headless Horseman statue. Since its debut in October of 2001, the overlay of the Haunted Mansion into “The Nightmare Before Christmas” has given Disneyland an attraction that essentially extends Halloween into early January.

Long before his current role in animation and as a Disney historian, Price worked in security at Disneyland Park.

“I worked at the parks during opening day of that attraction,” Price says. “Talking to the people who worked on this, they were very nervous. They didn’t know how the public would react. Guests rushed to the ride. We had to tell people to slow down. It really added excitement.”

It set the tone for how Disneyland would tackle Halloween at its two parks, one that isn’t scary but manages to embrace the holiday’s modern come-as-you-are or come-as-who-you-want-to-be ethos. Take, as an example, the decorations in Cars Land, where the hippie Fillmore is normally played for laughs. At Halloween, he becomes a full-on artist as his 2D metal art conjures a world of car ghosts and his organic fuel burns images into oil drums. Then there’s a zombie-like car outside of Radiator Springs Curios, which, as the story goes, is the result of a broken-hearted car trying to raise her husband from the dead.

Coupled with an influx of villains at the parks during the season, Halloween at Disneyland is a time to play at different versions of yourself. And that, say those who work on Halloween events, is what is at the heart of today’s multi-month observance of the holiday.

“I am someone who believes that every single person has a weird freaky side to them, whether that be voyeurism or just dressing up or being the story,” says JFI’s co-founder JT Swierczek. “During Halloween, people are allowed to be as weird as they want. I think Halloween allows people to be exactly who they are.

“Christmas is lovey-dovey and huggy and all that, but it is one-sided,” Swierczek continues. “What I love about Halloween, is there is plenty of room in the sandbox to do very different things all in the same theme.”

At Disneyland that can be, say, Mickey Mouse in a costume, or a car who wants her dead lover back.