The giant gartersnake is a federally threatened species endemic to California’s Central Valley. With the widespread loss of natural wetlands, this species has become significantly reliant on rice agriculture areas as crucial artificial habitat. Due to the snake's high site-fidelity to these chemically maintained areas, combined with a long lifespan and high trophic position, the giant gartersnake is an ideal candidate for studying pesticide exposure and bioaccumulation. We partnered with the U.S. Geological Survey to investigate the detectability of pesticides commonly applied in rice cultivation. We sampled tail tips from giant gartersnakes collected across the Sacramento Valley where rice agriculture was present or adjacent. To maximize our ability to detect low-concentration compounds, we composited samples based on similar capture size and location. Our analysis revealed notable pesticide concentrations in most of the composited samples (n = 41 detected ; n = 8 not detected). However, we did not find any significant statistical relationships between pesticide concentration or detection likelihood and the amount or time of application. The detection of one specific pesticide, which has been prohibited from application since 1972, strongly suggests that these compounds are persisting in the environment and are subsequently bioaccumulating in the giant gartersnake population occupying agricultural habitat. These results not only highlight a significant conservation concern, but also validate the valuable use of tail tips as an effective, non-lethal bioindicator for monitoring persistent pesticide concentrations in the species.