Two moorings deployed for 75 days in 2019 and long-term satellite altimetry data reveal a spatially complex and temporally variable internal tidal field at the SWOT Cal/Val site off central California due to the interference of multiple seasonally-variable sources. Coherent tides account for $\sim$45\% of the potential energy. The south mooring exhibits more energetic semidiurnal tides, while the north mooring displays stronger mode-1 M$_2$ with an amplitude of $\sim$5.1 mm. These findings from in situ observations align with the analysis of 27-year altimetry data. The altimetry results indicate that the complex internal tidal field is attributed to multiple sources. Mode-1 tides primarily originate from the Mendocino Ridge and the 36.5\textendash37.5$^\circ$N California continental slope, while mode-2 tides are generated by local seamounts and Monterey Bay. The generation and propagation of these tides are influenced by mesoscale eddies and seasonal stratification. Seasonality is evident for mode-1 waves from three directions. Southward components from the Mendocino Ridge consistently play a dominant role ($\sim$268 MW) yearlong. We observed the strongest eastward waves during the fall and spring seasons, generated remotely from the Hawaiian Ridge. Westward waves from the 36.5\textendash37.5$^\circ$N California continental slope are weakest during summer, while those from the Southern California Bight are weakest during spring. The highest variability of energy flux is found in the westward waves ($\pm 22\%$), while the lowest is in the southward waves ($\pm 13\%$). These findings emphasize the importance of incorporating the seasonality and spatial variability of internal tides for the SWOT internal tidal correction.