Career Highlights
• 2024 Second Team All-Big Sky
Career Summary
Spent four seasons at Cal Poly (2022-25) before transferring to UCLA ahead of the 2026 season … appeared in 34 games, starting 17, over four seasons with the Mustangs … totaled 195 tackles, 9.0 tackles for loss (TFL), 1.5 sacks, five forced fumbles, and two interceptions … earned second team all-league honors in 2024 at Cal Poly after co-leading the Big Sky with three forced fumbles and recording career highs in tackles (82) and TFLs (6.0).
2025 (Cal Poly)
Appeared in and started all 12 of Cal Poly’s games as a redshirt junior … notched 74 tackles (39 solo) with 3.0 TFLs, one interception, one forced fumble, and eight passes defended … had 14 stops, his most ever as a Mustang, at Northern Arizona on Nov. 15 … notched 11 tackles and an interception against Montana on Oct. 11.
2024 (Cal Poly)
Played in all 11 of Cal Poly’s games as a redshirt sophomore, starting three … named Second Team All-Big Sky … totaled 82 tackles, 6.0 tackles for loss, and one sack … had a season-high 12 tackles and forced a pair of fumbles at Idaho on Oct. 19 … his three forced fumbles on the season co-led the Big Sky … had a trio of 10+ tackle outings … had a season-high three TFLs, and 10 tackles overall, on Nov. 2 against Montana.
2023 (Cal Poly)
Played in two games as a true sophomore before an injury cut his season short.
2022 (Cal Poly)
Entered 10 games as a true freshman, starting two … totaled 36 tackles (26 solo) … posted a season-high nine tackles at Montana on Nov. 5 … added seven tackles in the season finale against Portland State on Nov. 19.
High School
Graduated from Kimball High School in his hometown of Tracy, Calif. in 2022 … named first team all-league as a senior … accumulated 1,429 all-purpose yards as a senior, making 73 catches for 1,259 yards and 16 touchdowns, intercepting seven passes for 30 return yards and two touchdowns, returning a punt 70 yards for another score and adding 70 yards in kickoff returns ... notched 69 total tackles (53 solo stops) as a free safety … also played baseball.
Personal
Full name: Mason Justis Rivera … parents are Tracy and Sean Rivera … has an older brother, Ryan, who played football at Cal Poly … enrolled in the project management certificate program at UCLA … aspires to become a firefighter … hobbies and interests include football, fishing, and gaming … admires Steph Curry … decided to attend UCLA because “the coaches here are great to be around and work with, and the program is one big family working together” … cites earning All-Big Sky honors in 2024 as his top pre-UCLA athletic highlight … majored in forest and fire science at Cal Poly … his family is his “why.”