Why is it called "Indian Summer?"

Summer, or what passes for it in the Pacific Northwest, was humming along nicely until we awoke to a downpour of biblical proportions (I will concede to my two typhoon livin' friends of the East). This cozy scene was the days following:

fall, originally uploaded by SJNedo.

Then, BAM! It's 85 degrees and the sun is shining to blind.

Plus, I have a gnarly cold that is keeping me from enjoying much of anything. (Life would be so tedious if you could not taste or smell.)

Indian summer go away! I want to wear sweaters and tights and shoes that keep the rain out.

Check back in a few months; I'll be crying like a tiny baby because this cursed region is so cold, dark and wet.