Delicious Fungi Volunteers

Lucky me!  Somehow I ended up getting some morel mushrooms in one of the moist sandy spots in the garden near my manzanita (Arctostaphylos peninsularis).  I think they're common (or white) morels (Morchella esculenta).  I wonder how they got there....I'd love to know how to keep them coming back and how to grow even more!

For identification and confirmation that this morel isn't poisonous - thanks to:
The Great Morel Homepage
Edible and Poisonous Mushroom Page by Barbara Bassett, Naturalist