I live in Berkeley, Ca. which part of the current range of the Coast Redwood ( Sequoia sempervirens). The current range is from just south of Big Sur, Ca. to just over the border into Oregon, from the coast to 60 km inland and from sea level to an elevation of 1 km. I've got one growing just 2 doors down from house.

In the distant past, before the beginning of the last Ice Age, the range was much larger. There are large stretches of the west coast of this continent the Coast Redwood should be growing. The 3 things that limit the redwood from growing are:

1. Rainfall: The redwood needs a lot of rain to grow to the giant size. Myers Flat, Ca. in Humboldt county, which is the heart of redwood county, gets 250 centimeters a year. There are many places on the west coast that get that much rain. Fork, Wa. gets 300 centimeters of rain a year.

Another factor to consider is when the rain falls. In Northern California beginning in May there are 4 to 5 months without rain. During these months the coast is covered in fog. Up to 30% of the rain a Coast Redwood receives is in the form of fog during these months. However, the further north one goes up the West Coast the more even the distribution the rain is.

2. Temperature: The Coast Redwood likes a mild climate, not too hot and not too cold. Myers Flat does not get much over 90 in August and rarely gets down into 20's overnight during the winter.
3. Soil: The coast redwood does very well in alluvium soil especially alluvium fans but the redwood will grow and thrive in any sort of soil as long as there is good drainage. It really does not like a heavy clay soil.

During the last Ice Age the glaciers advanced down from the poles. The Cordilleran Ice Sheet covered the Puget Sound area all the way south to Olympia. The distance from Olympia, WA., the appromate southern reach of the glacier, to the California border is about 570 Km. It is a safe assumption that the area near the glacier was very cold, too cold for redwoods. The last Ice Age ended about 11,000 years ago when the global tempature began to rise. But consider how the Coast Redwood propergates.

The Coast Redwood propergstes by seed and vegatiave. A redwood will produce thounds of seeds every year but these seeds are very small and they don't fall very far from the tree plus less than 5% of all these seeds ever sprot.