Riddle barely made it out of the qualification round but the Spruce Grove, Alta., native was strong in the final, taking gold with a score of 91.2. Aaron Blunck won silver and fellow American David Wise took the bronze.
Riddle, who has reached the podium in three straight events, said he just wanted to put down a strong, clean run.
"I couldn't be any happier with how it's gone," Riddle said of his season. "I'm just focused on my skiing day by day and not getting ahead of myself. I've been skiing the best that I ever have so I can't complain at all."
Soft snow in the bottom of the halfpipe meant athletes had a difficult time maintaining enough speed to get the sufficient amplitude to properly execute tricks.
Matt Margetts of Penticton, B.C., as 10th.
In the women's event, American Maddie Bowman won gold with a score of 84.6, finishing ahead of Calgary's Groenewoud in 79.2. Brita Sigourney of the U.S. was third with 79.0.
"Roz was definitely affected by the slow speed of the pipe," said coach Trennon Paynter. "She did a good job but just didn't have as much speed into her last two tricks to get enough height."
Calgary's Megan Gunning was fifth and Cassie Sharpe from Comox, B.C., was 12th.