California redwoods range

The California redwood (Sequoia sempervirens) natural habitat is essentially coastal northern California. According to Wikipedia, the northernmost point they can be found is only 15 miles north of the California-Oregon border.

Is there a reason it doesn’t grow further north along the coast?

Too cold and wet, plus wrong soil conditions. Redwoods are quite picky about their ecological requirements - mild tempertures, wet Mediterranean winters and abundant summer fog ( more important in the southern end of the range ) are necessary. In addition they tend to be confined to serpentine soils and a glance at an Oregon soil map will show that coastal serpentine stops not to far north of the border:

In general southern Oregon is grouped into the California Floristic Province, because of similarities of ecology:

http://www.nmnh.si.edu/botany/projects/cpd/na/map4.htm

  • Tamerlane

It gets quite a bit colder between Brookings, OR and Crescent City, CA.
Plus, the Coast Mountain Range begins right around there, and Douglas Firs start taking over.