Biologists have pointed to differences in received calls as evidence for some separation in finback populations in different locations [Watkins et al., J. Acoust. Soc. Am. 82, 1901--1912 (1987)]. More specifically, it has been concluded by Thompson et al. that the unique finback doublet interpulse intervals recorded in the Gulf of California constitute corroborating evidence for the hypothesis that ``Gulf of California fin whales may be a separate population, distinct from fin whales in nearby Pacific regions'' [Thompson et al., J. Acoust. Soc. Am. 92, 3051--3057 (1992)]. An alternative explanation is offered---that regional differences in finback doublet interpulse intervals may be accounted for by differences in acoustic propagation conditions. In this work, a broadband acoustic propagation code is combined with an empirically derived geoacoustic seafloor model for the purpose of interpreting finback doublet sequences recorded in the northern Gulf of California by Thompson et al. in 1987 [ibid.]. The result is that for ranges less than 30 km, it is possible to explain the appearance of the finback doublet in terms of multipath propagation through the water column and the seafloor. Further, the interpulse delay is demonstrated to be strongly range dependent. Scientists might consider the possibility that finbacks make use of multipath intervals to estimate distances to other finbacks, perhaps for reasons related to social behavior.