Accurate measurements of under cutoff proton fluxes in the energy range 0.07--9.1 GeV have been performed with the Alpha Magnetic Spectrometer (AMS) at altitudes of 370--390 km in the geographic latitude interval ¿51.7¿. A clear transition from a Stably Trapped population typical of the Inner Van Allen belts, in the region of the South Atlantic Anomaly (SAA), to a Quasi-Trapped population in the regions underneath the Van Allen belts outside the SAA is observed. The flux maps as a function of the canonical adiabatic variables L, αo, and energy E are presented and discussed.