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Rio Grande-Pecos and Guzman Basins Samples from these basins were primarily procured for outgroup comparison in mtDNA studies of Colorado Basin and Mexican populations and consequently are quite small. While the sample from the Rio Jemez in the upper Rio Grande (RGD) may be marginally ample (n=8), those from the Pecos (PEC) arm of the Rio Grande (n=4) and the Rio Mimbres of the Guzman Basin (GUZ) drainage (n=3) are small. Consequently, only preliminary observations can be made based upon them and such calculations as Hardy-Weinberg conformance are probably not meaningful. However, it should be pointed out that DeMarais (1992) examined much larger samples from these basins (but not Mexican Pacific drainages) and found similar results where the scopes of the respective studies overlap. Similarities and differences between samples from the Rio Grande-Pecos and Guzman basins and those from the Yaqui drainage to the south have already been discussed and those with the Colorado Basin will be discussed further in the succeeding section. Examination of the Rio Grande-Pecos and Guzman samples indicates, overall, a high degree of genotypic similarity between them and with samples from the Gila Basin to the west. UPGMA similarity analyses herein (Figs. 13-17) consistently place the Guzman sample in a grouping with Gila Basin samples to the west rather than with Rio Grande samples; in all cases, it was paired with the sample from the distant, now endorheic, Williamson Valley within the general realm of the Gila Basin. The Rio Grande samples (RGD & PEC), along with one sample (GAV) from the eastern Yaqui were more distant, forming a group which was paired with a grouping consisting of all Gila and Bill Williams system samples (e.g., Fig. 13) or, in some cases, all lower Colorado Basin samples exclusive of the Lake Mohave samples (e.g., Fig. 15). Similar analyses in DeMarais (1992) based on larger sample sizes paired the Guzman sample with a grouping of those from the Rio Grande. However, phylogenetic analyses performed by DeMarais consistently placed Guzman samples as a sister group both to Rio Grande samples and those representing several other species of Gila from the Colorado and other basins rather than to Rio Grande samples alone. Allelic Variation Possible fixed differences between the Guzman Basin sample and the Rio Grande-Pecos samples occur at the GPI-1 (faster 113" allele in former) and PK-1 loci (slower "1" allele in former as in Colorado Basin)(Figs. 7,12) pending examination of larger samples and additional populations in these basins. DeMarais (1992) did not examine PK-1 but found differences at "GPI-A" and lesser differences at two other loci not examined herein. Within the Rio Grande basin overall, possible allelic differences 7