Complex sentence: Matson & Coupland, 1995:64 The coastal migrants may have been followed by the Clovis culture when the final retreat of the Cordilleran Ice Sheet opened migration routes between interior and coastal Alaska.
Split into simpler sentences: Matson & Coupland, 1995:64 The coastal migrants may have been followed by the Clovis culture. With the final retreat of the Cordilleran Ice Sheet migration routes opened between interior and coastal Alaska.