A source near the deep sound channel axis excites mode groups (or paths) that involve both deep sound channel and boundary interacting propagation. Dispersion from a broadband source as measured on a single hydrophone can be used to estimate source range. Furthermore, modal group speeds have a functional transition when passing through purely refractive to boundary reflecting phase speed regions which, under certain conditions, provides additional arrival structure to aid in source localization. This additional arrival structure is in the form of a focal region in a spectrogram. Indeed, different data sets from the Acoustic Thermometry of the Ocean Climate (ATOC) Program [ATOC Consortium, Science 281, 1327-1332 (1998)] show that localization can be accomplished using this focal region and/or the overall dispersion properties as originally suggested fifty years ago [M. Ewing and J. L. Worzel, Geo. Soc. Am., Memoir 27 (1948)].