The Angels received minor league right-hander Erik Manoah.
Salas has a 4.47 ERA in 58 appearances for the Angels this year, but he has pitched to a 2.93 ERA in 17 appearances since the All-Star break. He has a ground-ball rate of 41.6 percent this season and also has six saves.
The 31-year-old made his major league debut with the St. Louis Cardinals in 2010 and was traded to the Angels following the 2013 season. In 374 appearances, Salas has a 3.71 ERA, a 1.18 WHIP and has totaled 30 saves.
He is expected to be added to late-inning mix that includes Addison Reed, who was acquired last August from the Arizona Diamondbacks.
Salas likely will be a rental for the Mets (69-64), who have won nine of 11 to get within 1 1/2 games of the St. Louis Cardinals for the second National League wild-card spot. He is making $2.4 million in his final season of arbitration eligibility.
Manoah, 20, has not advanced past Class A since being drafted in 2014. He was 5-5 with a 5.37 ERA in 13 appearances this year for Brooklyn of the short-season New York-Penn League.
To make room for Salas on the 40-man roster, New York moved outfielder Justin Ruggiano to the 60-day disabled list.
Ruggiano (left shoulder strain) was placed on the 15-day disabled list Saturday. It is the second DL stint this month for Ruggiano, who was out Aug. 2-18 due to a strained left hamstring.