Recently completed studies of neotectonic (ie., latest PlioceneQuaternary) deformation in Arizona provide new data that, when combined with regional geophysical and geological characteristics, assist in evaluation of the numerous interpretations proposed to date for Basin and Range tectonism. Basin and Range tectonism, sensu strictu, is hereby restricted to the post mid-Miocene (~15 m.y.B.P.) extensional block faulting event that produced the present valley and range topography. This tectonic interval may be distinguished in Arizona from earlier Oligocene-mid Miocene deformation and volcanism based on regional variations in stratigraphy and structural style.