One reason why a coastal route was postulated was due to the timing of the ice-free corridor. The timing of this ice-free corridor, or the timing of deglaciation, is crutial to the theory that the Clovis people spread south through an ice-free corridor (located between the two melting continental ice sheets) to colonize the rest of North America, namely the United States. Some people believe that there was no ice-free corridor available until much later after the Clovis people arrived. If the Clovis couldn't cross the mid-continental landmass via an ice-free corridor, then they must have travelled around this barrier going along the more accessible coastlines to reach south North America. Micheal Collins (2000) questions how the Clovis could have travelled 16,000 km in about 800 years through a 1,600 km long ice-free corridor from eastern Beringia to the southtip of South America. The dates do not appear to fit. Language development in such a short time, and the distribution of Clovis artifacts do not support the ice-free corridor theory (Collins, 2000; Hofman, 2000). A lack of bone fossils dating between 21,000-11,500 ya in the area believed to be the location of the ice-free corridor indicates that the ice-free corridor was not established until 11,000 ya (Hofman, 2000). In short, the Clovis people as the first peoples to the Americas arriving 15,000 ya could not have travelled via an ice-free corridor that was available only 11,000 ya to colonize the south where fossils of the Clovis culture found in the United States date before 11,000 ya.
Supporters of the Clovis expansion believe that the ice-free corridor was open through the late glaciation or that it was closed briefly. Canadian geologists have shown that the corridor began opening up 13,000 ya, and was hospitable for crossing between 12,000-11,000 ya. It may have been 25 km wide. Clovis artifacts and the entire assemblage of Ice Age fauna have been found associated together in the United States between 13,000-11,000 ya (Haynes Jr., 2000). These dates somewhat support the ice-free corridor hypothesis. The water table is believed to have fallen drastically during this time, and Pleistocene fauna became extinct. These fossils were found buried in a former water environment which suggests transportation of the bones. What is interesting about this find is the correlation of the Pleistocene megafauna and Clovis extinctions to the Younger Dryas strata which is marked by dark mats. Neither are present in the Younger Dryas stratigraphy (except for Bison).