Mengden was optioned to Triple-A Nashville on Tuesday, John Hickey of Bay Area News Group reports.
Mengden had an atrocious July, giving up 17 walks, 31 hits, and 23 earned runs over his last five starts, leading to a 9.00 ERA and 2.09 WHIP for the month. He'll head back to Triple-A Nashville and look to regain the form he had in June. J.B. Wendelken was recalled in a corresponding roster move.