California water resources are heavily dependent on the precipitation associated with atmospheric rivers (ARs). This study is a 20-yr cool season (October-March) climatology that examines the vertical distribution of (IVT) in ARs over the Russian River (RRW) and Santa Ana River Watersheds (SARW). Cool-season precipitation data from PRISM is averaged over the RRW and SARW for the 20-year period 1999-2019. IVT magnitude and direction are calculated using water vapor flux and wind data from NASA MERRA in 50-hPa layers at 38°N 123.125°W for the RRW and 33°N 117.125°W for the SARW. AR events with IVT magnitudes greater than 250 kg m-1s-1(IVT250 events) in the RRW generate up to ~70% of total annual precipitation and generate up to ~60% of total annual precipitation in the SARW. The vertical structure of IVT250 events is analyzed to investigate the distribution of water vapor flux in the lower troposphere (1000-700 hPa), the upper troposphere (700-300-hPa), the direction of IVT relative to terrain, and precipitation totals. IVT concentrated in the 1000-700-hPa layer, and southwesterly ARs explains 73% of the variance of precipitation totals in the RRW and 48% of the variance in the SARW.