Bookwalter fell short of victory, finishing fifth on the day, but he took consolation in watching friend Andrew Talansky (Cannondale-Drapac) ascend to the top of the podium.
"I could tell Talansky was strong," Bookwalter told Cyclingnews. "I'm proud of him for winning. He's my buddy. I was in his wedding a few years ago and we're pretty close. He's had a little bit of a rough year, so it was nice.
"I was hoping I could take it to him, but good riding to him. If I can't do it, I'm happy for him."
Bookwalter was part of a select group that arrived at the bottom of Mt. Baldy together, eventually reeling in escapee Rob Britton (Rally Cycling) and setting off on a battle royale for the queen stage honours.
Multiple attacks from Talansky jettisoned Bookwalter from the lead group in the final kilometres, with Talansky, overall leader Rafal Majka (Bora-Hansgrohe), Ian Boswell (Team Sky), George Bennett (LottoNL-Jumbo) and Lachlan Morton (Dimension Data) going clear.
At the finish, Talansky nipped Majka for the win, Bennett came in next, followed by Boswell and then Bookwalter eight seconds down.
"I was actually more comfortable than I thought in the flatter spots in the first two kilometres," Bookwalter said, adding that the final steep switchbacks in the final three kilometres were his undoing.
Despite missing out on the win and the opportunity to cut precious seconds from his rivals ahead of Friday's 24km time trial at Big Bear Lake, Bookwalter remained optimistic about his and his team's chances.
"We came here with big ambitions to win, and we're a little off," he said. "But we still have an important time trial stage tomorrow, and I think anything is still possible."