Geological events such as the formation of rivers and mountains can drive diversification. We here test vicariant hypotheses using the primitively segmented spider genera Sinothela and Ganthela, focusing on diversification within Sinothela. Our results suggest vicariant origins of Sinothela and provide evidence for continental-wide vicariant events that have shaped these spiders’ evolutionary history in continental East Asia. Our study also highlights how dated molecular phylogenies can narrow down too widely estimated time intervals of river and mountain formation by geologists. Primitively segmented spiders thus provide an excellent model for exploring how geological events shape biodiversity.