Our silvery mystery seeds from last week were from Lindley's silver puffs, Microseris lindleyi.
I have to admit these were tough ones to identify. I have only seen them at the Desert Botanical Garden on the wildflower trail and in a botanically-minded friend's yard. They do grow throughout the western United States, however.
The seed heads are somewhat reminiscent of a dandelion, but the parasol is thicker and silvery in color.
I don't have any photographs of the flowers, but they have interesting pointed green bracts that make them look star-shaped, giving them their other common name "starpoint." Firefly Forest has photographs of the silver puff plant and flowers. Wildflowers in Santa Barbara also has silverpuff photographs.