Spoiler alert: Monday’s “Mark Trail” installment includes a surprise.

This is no longer your grandparents’ — or your parents’ or even your own — Mark Trail. This is a 21st-century version of the hard-hitting defender of the environment.

The Monday strip is the first by a new artist who has taken over the iconic comic strip. Jules Rivera, whose versatile background runs from sci-fi and adventure graphic novels to slice-of-life comics, is launching her new gig with a bang.

“There’s a shock in the last panel,” the Los Angeles-based artist warned. “It was accidental, but when I saw it, I was glad it’s there. We’re calling out Mark Trail. We’re moving forward, and fans [of the strip] have to get ready.”

And it won’t be the last shock for Trailheads. “There are going to be jolts galore,” she promised. “Jolts is my brand.”

That being said, she’s also assuring the strip’s loyal readers that she’s not jettisoning everything that has made “Mark Trail” part of their daily routines since 1946.

“I want to respect the legacy,” she said of the long-running strip. “I want to keep what made ‘Mark Trail’ great. I appreciate what the fans appreciate,” including the title character’s love for nature and dedication to protecting the environment.

Speaking of surprises, no one is more surprised than Rivera that she’s taking over the strip. It wasn’t at all on her radar.

“It’s something I never thought I’d be doing,” she admitted.

She was approached by Tea Fougner, the editorial director of King Features, the syndicate the handles the strip, who had seen Rivera’s digital comic, “Love Joolz.”

“Jules’ work speaks for itself, and her passion for both conservation and comics makes her an ideal fit to reimagine Mark Trail,” Fougner told the online comics magazine the Beat. “Her thoughtful yet humorous approach makes environmental issues accessible, educational and fun while also honoring Mark Trail’s roots as a classic adventure comic.”

Rivera is only the fourth artist in the strip’s history. It was created by Ed Dodd, who drew it until his death in 1978. Jack Elrod oversaw the strip until he died in 2016. James Allen replaced Elrod, but he and King Features announced in June that they had mutually decided to end the relationship.

A trailblazer

Rivera, 37, is of Puerto Rican descent. She is the lone Latinx producing a daily newspaper comic strip, a field that is almost solely the domain of white males. But she’s not intimidated by that because she’s been in that situation before.

Although she’s been passionate about drawing since childhood, she was concerned that she needed a career that was more stable than freelance art, so she became an electrical engineer.

“There are not a lot of women of color in STEM professions,” she said. “Back in the early ’90s, we were told that there was no more racism, that we had fixed the problem, that we were all equal now. And I believed it. Well, we haven’t fixed it. We’re not all treated equally. I didn’t know that I was walking into a snake pit.”

Encouraged by the reaction she was getting to the art she did on weekends and evenings, she quit her job in Florida, moved to Los Angeles and enrolled in the Gnomon School of Visual Effects to study animation and digital painting.

But she never entirely left behind her engineering background. When asked if she would “audition” for the Trail job by doing some test panels, she delved deep into the strip’s history.

“I researched and researched and researched,” she said. And then she analyzed the data to figure out what had worked and what hadn’t. She kept the former and booted the latter, which is why she refers to the newly configured strip as an “update” rather than a reboot or a makeover.

She also approaches the creative process for the strip like an engineer.

“I move forward with a very regimented plan,” she said. First she lays out the arc of the entire episode, then she goes back and breaks it into weekly segments. “I treat it in week-by-week chunks, and I want each chunk to move the story forward. It helps me stay organized, and it keeps the audience in a rhythm.”

Leaving a mark

Although at an age where she could shepherd the strip for several decades, she isn’t ready to set her sights on matching the tenures of Dodd (32 years) or Elrod (38 years), but she is determined to oversee the franchise longer than Allen’s four years.

“I want to make my mark,” she said. “I want to give something to ‘Mark Trail.’ I get to tell about nature, but I also want to talk about plants — I’ve gone a little nuts with gardening lately.”

She also intends to work Mark’s wife, Cherry, and their son, Rusty, into more stories.

While she’s devoting the bulk of her time to launching her version of “Mark Trail,” she’s not abandoning her other projects, including teaching movie storyboarding at California Lutheran University. She also intends to keep producing “Love, Joolz,” which she describes as being about “hard truths, weaponized femininity and screaming at the sky.” (The strips are posted twice weekly on webtoons.com.)

So far, at least, she’s gotten surprisingly little pushback about a woman taking over a story about an environmental he-man.

“The day the news dropped, I was pretty sure that I was going to face an inbox of hate mail,” she said. “But the fans have been very supportive in their response.”

That might have something to do with the promise she made when she took the job.

“Just because I’m a woman doesn’t mean that Mark Trail isn’t going to do any more punching.”