Given its appearance and your description of its blooming habits, chances are it's Crimson King (a species or natural hybrid collected by Barr in 1893).

From the 1925 Cornell Extension Bulletin 112: "Color effect an intense violet-purple self. Standards pansy violet, lighter to yellowish claw and wavy along the edge. Falls continga purple, almost velvety in texture. The veining is boldly spaced on whitish outer haft, while those on Kochii are not so prominent. Its fragrance is good, its color very intense, and its spathe valves deeply tinged. The persistant green foliage is attractive in winter."

I live in northern California too - it blooms and reblooms like crazy around here, probably more than any other iris, and I see it in many gardens.

Jean

Jean - thanks so much! I have looked up several photos/descriptions of Crimson King, and it certainly does look and sound like my iris (bloom time, and the fact that it multiplies like rabbits). My Father-In-Law's grandmother, who he said planted it here, lived in our house from 1905 until her death in 1911, so the dates make sense too.

When we first moved here I didn't know anything about plants or gardening. There were all of these spikey leaves growing under a thicket in the dark. He showed me how to move them to the sun, and to my amazement they bloomed into this iris the following Spring!

Jackie

Yes, it is Crimson King; a weed in California; always in bloom. You will find it everywhere.