Renewable natural gas has the potential to diversify and decarbonize natural gas as a transportation fuel. Biomethane, a subset of renewable natural gas, is produced from a range of waste sources that are distributed across the landscape with uneven access to natural gas infrastructure. Using a spatially explicit techno-economic model of renewable natural gas supply in California, we develop supply curves for producing renewable natural gas and delivering it to California's transportation fuels market in order to estimate the economic potential. The gross potential is 90 bcf per year (94.5 PJ/yr), which is larger than the 17 bcf per year (18 PJ/yr) of natural gas consumed as transportation fuel in California in 2016. Seventy-five percent of the resource is estimated to be economic if the value of existing policy credits are fully capitalized, resulting in 6.9 million Low Carbon Fuel Standard credits. Renewable natural gas provides an economically viable option for methane emission reduction for a quarter of dairy manure in the state. The results suggest that renewable natural gas can play a significant role in meeting low carbon fuel policies in California and that expansion of demand for natural gas in transportation is needed to fully realize this potential.