Alaska, yes. But you have some pretty mild climates in the Pacific Northwest and all the way down the California coast. The Chumash tribe, centered around present day Santa Barbara, never put up anything even close to the Inca, Maya, Aztec, Toltec and a score of others further south.
But that would imply that people built the most elaborate culture at the first place they stopped. I am saying it is more geopolitical. That region of Central America seemed optimal to them and allowed them to build a more elaborate civilization. Why was their no Greece or Rome in Scandinavia?
Now we do. Thirteen thousand years ago the ice sheets extended all the way down to the present location of Seattle, and there was a mighty river that flowed from the ice sheet in that location, down to present-day Aberdeen, on Grays Harbor bay.
The Pacific coastline thirteen thousand years ago extended out 26 miles from the present day coastline, and there was land between present-day Alaska and Siberia. Migrants would have followed the coastal plain down to the Columbia River which gave access to the eastern plains of present day Washington and Oregon, but that was risky as flooding occurred regularly. See; Catastrophes on The Columbia, which explains why the mammoths, woolly rhinoceros and horses disappeared from the area. Over a period of five thousand years there were periodical floods resulting from the ancient Lake Missoula emptying.