Her concession came after Riverside County released updated vote totals showing Ruiz, a Democrat, had widened his lead to more than 7,000 votes.
The race in the desert communities near Palm Springs was one of this year's hottest congressional battlegrounds and drew millions in outside spending.
Bono Mack is the wife of Florida Congressman Connie Mack, who failed Tuesday night in his attempt to gain a Senate seat. Bono Mack was elected in 1998 to the 36th District following the death of her husband, entertainer turned Congressman Sonny Bono.
Ruiz is an emergency room doctor and son of migrant farmers. Ruiz said he credits the community for bringing him this far. Re-districting may have also played a part in what may be a victory for Ruiz due to the inclusion of more independent voters.