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Photo: Diane Edwardson, February 28, 2013. I did not realize this was a Monarch Butterfly until I downloaded the photos. All I saw was a large orange butterfly. I was shooting from 10 yards away, while it was feeding on non-native, invasive Wild Radish flowers, at the north end of the Red Car Property, above the historic viaduct footings. (Shoot first, ask questions later. Click on photos to enlarge.)
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Monarch populations are declining due to deforestation and Milkweed die-off. (Native Kotolo Milkweed grows on the northern end of the red Car Property. It is a slow growing plant that often gets destroyed, before going to seed, when the City does brush clearance with a bulldozer.)
The Natural History Museum only shows photos of 8 species of butterflies on their website. So here's a few other resources for identification & education:
Butterflies and Moths of North America
BugGuide
Butterflies & Their Larval Foodplants (UCI)
Monarch Watch