A realistic 3D seismic velocity model plays an important role in wave‐propagation simulations for estimating ground motions from damaging earthquakes. In addition, the 3D velocity variations associated with sedimentary basins are particularly important. Recent updates on the Community Velocity Model (CVM) for southern California made through crustal‐scale full‐3D seismic waveform tomography (F3DT) have improved the basin structures substantially. The basin structures in the updated 3D velocity model CVM‐S4.26 exhibit high correlation with surface geology, independent gravity measurements, and 2D controlled source tomography profiles. The improvements in basin structures are reflected in the much‐improved fits between synthetic and observed waveforms that are sensitive to basin structures. Seismic‐hazard analysis based on either empirical approaches or numerical simulations can potentially benefit from the improvements in basin structures in CVM‐S4.26.