Receiver functions from teleseismic events, recorded by stations around the Gulf of California,
are used to map the upper-mantle seismic discontinuities. We observe a mean transition zone
thickness comparable to the global average for most of the region. A low-velocity layer is
detected above the 410 discontinuity that varies in thickness along the Gulf of California. The
660 discontinuity shows complex waveforms south of latitude 30◦N as a result of the phase
change of garnet to perovskite. Within the transition zone, a complex behaviour of the receiver
functions is observed mainly at the southern end of the Gulf. The north–south variations of
this zone are likely associated with a slab window at the northern Gulf, resulting from the
cessation of subduction of the Farallon plate 12 Ma, and the subduction of the Guadalupe and
Magdalena microplates at the southern end, resulting in a hydrated upper mantle. Our results
suggest that change in rifting styles occurring along the Gulf of California mirrors deeper
processes in the upper mantle
