While working toward his bachelor of science in applied mechanics and engineering sciences from the University of California San Diego (UCSD), Bonita, CA’s Mario X. Sierra mentored local high school students through the Early Outreach Program and supervised UCSD tutors as a coordinator with the Oasis Program. Mario Sierra also co-founded the UCSD chapter of the Society of Hispanic Professional Engineers and held membership in the UCSD chapter of MEChA (Movimiento Estudiantil Chicano de Aztlan).

After working as an engineer in the private sector for several years, Mario X. Sierra joined the City of San Diego in 1989 as a building inspection department plan review specialist. He subsequently accepted a series of rapid promotions.

While employed by the City of San Diego as a deputy director in its Street Division, Mr. Sierra returned to the academic environment to secure a master of arts in public administration from the National University. As the director of the City of San Diego Environmental Services Department from 2014 to 2019, he oversaw 420 employees and a budget of $105 million.