When he isn't riding across the country, Sullivan works for The International Liberty Horse Association as a judging coordinator. According to the organisations website, their goal is to "highlight the physical and mental ability of horses to work completely at liberty – free of all tack and equipment,"
Sullivan's horse Gamilah is a "liberty horse," meaning she is trained using positive reinforcement and clickers rather than saddles, bridles, ropes or reigns.
The ride wasn't purely for pleasure, as Sullivan said they were doing it for the greater good, stopping off at 17 farms, horse rescues and charities during the journey and teaching them about the value of a human-horse connection.
"We are doing it all for nonprofits," Sullivan told new company WDRB while passing through Lousiville.
"So, we started our own nonprofit called Gamilah Unbridled. It's for underprivileged kids and literally teaching how horses and heal people and people heal horses."
As one can imagine, the journey hasn't been easy, as the pair endured snow, rain and temperatures of over 38 degrees in states like Utah and Missouri.
"Everybody thought I was completely crazy," Sullivan said, "probably because I am."
From urban cityscapes to dusty deserts, the pair have loved seeing the reactions of people they meet along the way.
"Usually it's a double-take: Not only are we riding a horse, but it's also bridle-less," Sullivan said, adding that many people couldn't work out how he steered his partner.
The trip from California had been a long one but Sullivan said rest days had been key for recovery, especially when he wasn't the one doing all of the work.
"I'm just along for the ride, literally," he said.
Although the purpose has been to give back, Sullivan said it had been a dream come true for him.
"I just can't put into words how much these horses have given to me and the people that we've met have given to me. That is really just a blessing, and it's something that I'll remember for the rest of my life. "
Sullivan and Gamilah have a few more miles to cover, attempting to finish at the Kentucky Horse Park in Lexington on October 22.