Do they call the California shift the California shift because it 1) exists mostly just in California or 2) originated in California and is spreading to other areas such as Oregon, Nevada, Arizona or 3) because California English is better studied than other areas and other areas have as much of the shift or 4) is it a shift that only affects certain groups (determined by gender and age) in California and other areas to the same extent?
California shift
Since the Canadian shift also exists in the West, how would they tell if a speaker had the Canadian shift in California vs. the California shift?
Canadian shift is, normally, more spread. Californian newscasters and actors don't have the Californian shift (or they have 1-2 out of 5 elements of the shift). It's is not a mainstream thing, it's restricted to certain social groups (Valley girls, for example). In Canada, most newscasters have the Canadian shift. Also, most people in Canada have the Canadian raising (absent in California), so Rider and Writer are not pronounced the same in Canada.