In high school, Upshaw played for Pittsburg High School (Pittsburg, California), helping defeat the previously undefeated De La Salle in the 1991 NCS championship game played at the Oakland Coliseum. The final score was 35-27. This was the last defeat De La Salle suffered before setting a national high school record of 151 straight victories. Upshaw, who did not play football until his sophomore year at Pittsburg, was a Parade All-America as a senior. He chose the University of California and by his junior year was named All-American.