This section is from the book "The Gardener's Monthly And Horticulturist V24", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
As to the Fremontia ripening its seeds at the highest altitude I mentioned, it does so in all probability; otherwise how does it propagate itself? I never looked for seed there, because I could get it nearer home.
The Dendromecon rigidum grows near here. The handsomest plants I know are on the plains near the hills, but it also grows pretty high up. The highest altitude I know of its occurring, is between 3,000 and 4,000 feet above the sea ; scarcely high enough for it to be safe for Northerners to try it, but it is credited with growing at Clear Lake, which would give some hopes of its doing well. Southerners, if they care for such things, could raise it. It ripens seed here. It stands transplanting; at least the plant I bought this spring is growing.
Cowania Mexicana has never been found in California. The "Botiny of California" says: "Mountains of the Virgen river, California, Fremont (probably in Nevada)." But the Virgen as I well recollect, is in Utah. We have no Virgen river in California, "also in the mountains of northern Utah and New Mexico." From its habitat it will most likely prove hardy with you.
I am glad to see that my article has drawn the attention of at least one. Perhaps the fowls of the air may yet roost in the branches of my Mustard tree plant.