We propose an Exploratory/Developmental Research Grant (R21) in response to “Public Policy Effects, on Alcohol-, Marijuana-, and Other Substance-Related Behaviors and Outcomes” (PA-17-132) which calls for studies of local implementation of state marijuana and opioid policies and their impacts on substance use outcomes. Across the US, there is a trend toward liberalizing marijuana policy and addressing the opioid crisis. The effects of cannabis legalization on health outcomes are not clear and preliminary evidence suggests this may be due in part to local heterogeneity. Our work aims to develop a classification of local substance use policies in California. California provides an ideal context for this study because its laws regarding cannabis grant enormous latitude to localities to tax, limit, or ban retail and commercial businesses; unlike in other states, there is no cap on local cannabis tax rates. Further, California is one of 16 states authorizing syringe exchange programs (SEPs); as a result over 20 counties and cities have passed, opposed, and passed and rescinded SEPs. We propose a developmental R21 study that will map heterogeneity in the implementation of cannabis policies in 12 California counties, controlling for opiate policies, and then explore associations with health outcomes related to cannabis and prescription opioid use.