CK,
>>Their data shows that the Sierra Nevada subclade is confined largely to the western slopes of the Sierra Nevada mountains, and the general direction of the expansion of the range (gleaned from the mtDNA data) of this subclade is from south to north. In hindsight, you are correct, they did not consider the possibility that the Sierra Nevada subclade may have expanded its range eastward into Nevada to possibly meet the Northwestern subclade in western and central Nevada. Their mtDNA sample did not address this possibility>You may well be correct that allopatry is an artifact of observation. Sometimes we do forget what Robert Inger once said, and I paraphrase him here: the distribution map of the rubber boa is more likely to be a distribution map of human collectors.