Land bridges were once theorized to have connected the northern Channel Islands to the mainland, because it was assumed the mammoths could not swim. "
A land bridge between the mainland and Santa Rosae did not exist during the Quaternary"; however, the distance to the mainland was reduced to 7 km.
When the Ice Age caused the sea levels to lower, the four northern Channel Islands formed a single island that was closer to the mainland and also larger in size.
Pygmy mammoths are descendants of the Columbian mammoth.
These were capable swimmers able to swim to the new island and adapt to the new environment.

The pygmy mammoths lived on Santa Rosae island which was beginning to shrink due to rising sea levels.
The pygmy mammoths evolved through generations in order to survive on the ever-shrinking Santa Rosae Island.
Smaller bodies require less food and resources to remain healthy in a smaller territory and allowed for less competition among the species, which is an example of island dwarfism.
Also, their mainland predators such as the dire wolves, the Smilodon and the American lion were not present.
After this evolutionary period, the mammoth had become a distinct species, the pygmy mammoth.
The pygmy mammoth's evolution on Santa Rosae took over 30,000 years.
Land bridges were once theorized to have connected the northern Channel Islands to the mainland, because it was assumed the mammoths could not swim. "A land bridge between the mainland and Santa Rosae did not exist during the Quaternary"; however, the distance to the mainland was reduced to 7 km. When the Ice Age caused the sea levels to lower, the four northern Channel Islands formed a single island that was closer to the mainland and also larger in size. Pygmy mammoths are descendants of the Columbian mammoth. These were capable swimmers able to swim to the new island and adapt to the new environment.
The pygmy mammoths lived on Santa Rosae island which was beginning to shrink due to rising sea levels. The pygmy mammoths evolved through generations in order to survive on the ever-shrinking Santa Rosae Island. Smaller bodies require less food and resources to remain healthy in a smaller territory and allowed for less competition among the species, which is an example of island dwarfism. Also, their mainland predators such as the dire wolves, the Smilodon and the American lion were not present. After this evolutionary period, the mammoth had become a distinct species, the pygmy mammoth. The pygmy mammoth's evolution on Santa Rosae took over 30,000 years.
Pygmy mammoth