Bingham (20-0, 9-0) allowed just one basket in the final 3:30 to pull away after Riverton (17-3, 6-3) trimmed a double-digit halftime deficit to just four on a Shelby Richards layup midway through the fourth quarter.
Powell scored a season-high 22 points after being one of eight seniors honored in a pregame ceremony. Despite a plea from coach Rand Rasmussen to save the tears for later, several Miners welled up before playing their final home game.
"We knew we were going to be emotional," Powell said. "We just tried to push it out of our minds and worry about the game."
The Miners forced 18 turnovers on the night and held Riverton to just 4-of-24 shooting in the opening half to build a 23-10 lead.
"I said at halftime that [Riverton's] going to make a run and you have to answer," Rasmussen said. "We did to a point. … When you're playing Riverton and [coach] Ron Ence, you're playing somebody that's preparing you for the tournament.
"Playing their kids with how good a defense they play is going to help us down the road."
Jamie Smith hit back-to-back 3-pointers as the Silverwolves chipped away, only to have Powell connect for two of her four 3-pointers and maintain Bingham's lead.
Bingham has a chance to secure an unbeaten regular season Tuesday at American Fork before turning its sights on its fifth state title, and first since 2007.
Storylines Bingham 42, Riverton 35
R The Miners improve to 20-0.
• Bingham builds a 23-10 halftime lead by holding Riverton to 4-of-24 shooting.