A growing number of jurisdictions are passing ambitious clean energy policies. Yet few studies have accounted for natural and agricultural land impacts of low-carbon pathways and how environmental siting constraints affect electricity costs and technology choices. To address this gap, we developed an integrated land-energy planning framework to examine the land use trade-offs of renewable energy development required to achieve ambitious clean energy goals, using the state of California as a case study. Using high-resolution ecological and agricultural datasets for 11 Western U.S. states, we modeled environmentally-constrained onshore wind, solar photovoltaic, and geothermal potential and used an electricity capacity expansion model to build generation portfolios for 2050. Here we show that California can meet its targets, but the technology mix, spatial build-out, and system costs are sensitive to land protections and availability of out-of-state renewable resources. Results suggest that failure to consider land availability in energy planning could increase uncertainties, environmental impacts, and risks in meeting subnational climate targets.