Last season, Katie Rainsberger conquered the state of Colorado. Now, she’s taking her dominance to the national level.

The Air Academy senior – who is the defending 4A Colorado cross country state champion – posted the fastest time of any high school girl in the nation for the 2015 cross country season Friday.

Rainsberger’s 5K time of 16 minutes, 23 seconds at the Desert Twilight XC Invitational in Casa Grande, Ariz., is tops across the country.

“It’s kind of surreal, and really exciting that the hard work the past four years has amounted to something incredible,” she said. “The years of my persistent hard workouts have compiled and I’m starting to see it come together. It’s exciting, but the season isn’t over yet, and I have to keep at it.”

Rainsberger says being the top runner in the nation wasn’t necessarily a goal she was striving for, but that after her winning performance at the Coronado Cougar Invitational the weekend before, she felt like a big race was on the

“The last 800 meters in Arizona is a straightaway, and when I was coming toward the finish line I thought it said 16:50 and not 15:50, which made me angry, so I ran even faster,” she said with a laugh. “The fastest time in the nation before me was 16:31, so I wasn’t gunning for it, but I knew what it was in the back of my mind.”

During her four years at Air Academy, Rainsberger has become one of the most prolific runners in Colorado high school history. As a freshman and sophomore, she finished second in the state at the cross country finals, and crushed the field last season to win state.

Couple those accolades with her multiple state titles in track and field distance running, and most major Division I programs were knocking on the door. She’s narrowed it down to Michigan, Oregon and Stanford, with signing day upcoming Nov. 11.

“I was looking for a school where I’d have a good relationship with the coach and all the girls on the team, and where everyone is going for the same goal,” Rainsberger said. “An education is what’s most important to me. I want to go premed, and I’m not sure which route I’m going to take yet, but all three schools have really good premed routes.”

The key for Rainsberger to go from an elite runner at the state level to nationally was a change to her diet.

“I recently cut out gluten,” she said. “I was anemic at the end of last track season, so now cutting out gluten has allowed my iron levels to rise. That’s been a big part of it, but moreover, the small things I do after each practice and race has led to where I am now – things like drinking a lot of water and stretching.”

So when it comes to defending her 4A state championship in a few weeks, what keeps Rainsberger motivated when she’s such a heavy favorite to win?

“There’s always somebody out there better than you, whether it’s a high school runner or a college runner,” she said. “They aren’t taking any days off, so I can’t either.”