This article brings critical and postcolonial theories together with extended ethnographic research in a predominantly Latinx high school in California's "South Bay" to theorize the co-production and co-naturalization of mathematical and racial essentialization. Analysis of vignettes and interview excerpts illuminates both student uptake and resistance to homogenizing narratives of mathematics and racial personhood. Student voices from Sierra High School both evidenced the existence, stakes, and personal consequences of narrowly bounded, taken for granted, conceptions of mathematics and racial personhood and challenged these homogenizing categories. This paper contributes theory illuminating the co-construction of mathematical and racial essentialization along with examples of local critique and resistance from youth and their adult allies at one high school in the USA. Implications suggest that decolonial work in mathematics education must jointly address the narrow and essentializing frames for race and racialization and for mathematics itself as co-producing and co-naturalizing each other. This study contributes insight into mechanisms that perpetuate and also resist or disrupt these processes.