Coastal California captures a wide array of microclimates and unique vegetation zones, many of which are vulnerable to modern climate change. There is no clear consensus about how hydroclimate, or the seasonality, amount, and severity of rainfall, will change in response to rising temperatures. Increased rainfall variability has direct impacts on fragile ecosystems. We use long chain fatty acids from terrestrial vegetation to create hydrogen (δD) and carbon (δ13C) isotope records spanning the Last Interglacial along the California margin, on a latitudinal gradient from site 1012B (32⁰N) to Clear Lake (39⁰N). The Last Interglacial is cited as a good analogue for modern climate change, and these paired proxy records provide insight into hydroclimate and vegetation changes in response to climate change. We find considerable δDp enrichment at site 1012B and Clear Lake during the peak of the Last Interglacial (MIS5e) that is consistent with other hydroclimate records from the western US. Despite similar δDp signatures, we propose different hydroclimate change mechanisms for the isotopic shift. At site 1012B, increased sea surface temperatures on the southern California margin led to convective summer rainfall, resulting in enriched leaf wax δDp values, while Clear Lake δDp changes are more likely linked to changes in northern California upwelling strength. δ13C values indicate there was not a prominent shift in plant functional type during the time examined in either site, however, high resolution pollen records are paired with isotope data to show ecosystem changes in response to rising temperatures and shifting hydroclimate regimes. Rising sea surface temperatures on the California margin are likely to change rainfall patterns in the future. The Last Interglacial elucidates key climatic and ecological processes and yields insights on how coastal California ecosystems may be impacted by modern climate change.