Stokes, who turns 31 on Tuesday, made just 16 appearances this season and only one since May 9. He went on the disabled list with right shoulder fatigue on May 10.
Trumbo, a 24-year-old Anaheim native, hit .301 with 36 home runs and 122 RBIs at Salt Lake, which finished its season in second place with a 3-1 home loss to Reno on Monday, 1 1/2 games behind Tacoma in the Pacific Coast League Pacific North division. The Angels waited to make their callups because the Bees were still in the playoff hunt.
"He's certainly one of the top power prospects in baseball," Scioscia said of Trumbo. "He opened up a lot of eyes with the year he had in Salt Lake. ... Sometimes guys with big swings, it takes a little longer. I think whatever opportunity Mark gets right now isn't going to define him as a player."
Palmer is to work out of the bullpen, barring an injury to a starter. Scioscia said no other callups would likely be made.
Acquired by trade from the Mets for Gary Matthews Jr., Stokes finished his lone season with the Angels without a decision and an 8.10 ERA. He struck out as many as he walked, 16, in 16 2/3 innings.
"Brian is a guy that we just don't see the opportunity to pitch and move forward for us," said Scioscia. "He came out of Spring Training, I don't think he was ever really in sync."
Stokes said he didn't know what was next for him, but was glad to have some time left in the season to perhaps latch on with another club.
"I haven't really thought that far ahead yet," the California native said when asked where he goes from here. "I guess to my car, and figure it out tomorrow."
Stokes exchanged hugs with other members of the bullpen before leaving.
"He's one of the nicest guys I've ever met," Francisco Rodriguez said. "He got hurt and it was a rough year for him."
Told it was Stokes' birthday Tuesday, Rodriguez said: "It is? Oh my God. Even worse."