|Are marigolds perennial?
|There actually is a perennial marigold so that might be what you are growing. Tagetes lemmonii has a variety of common names including Lemmon's Marigold, Mount Lemmon Marigold, Shrub Marigold, Mexican Bush Marigold, Mountain Marigold, Alamos Marigold, and finally, Copper Canyon Daisy, which appears to be the preferred common name in this area. You might do a little research on the web to see if the photos of Tagetes lemmonii match your plants. It's likely these plants are spreading from seeds, either blown about by the wind or deposited by birds. Either way, enjoy your marigolds!