what kind of mushroom is this?

What kind of mushroom is this i live in southern california and i added mulch to my garden and in the parts that got shade these mushrooms sprouted.

not that i have any idea what it is, but i believe it helps if you get pictures of the gills underneath, the young and fully mature mushroom and the mushroom when cut lengthwise so as to show the stem interior and the interaction of the gills to the stem... you could also try:
http://mushroomobserver.org/?_js=on&_new=true
http://www.mycokey.org/agaric1.shtml?language=uk&localLanguage=uk&searchMode=easy&atlasmode=false&r=62493.89415022355

Although I wouldn't bet the farm on it (or my life), I would guess you might have something in the Panaeolus genus, perhaps Panaeolus subbalteatus- commonly found on compost or manure mulch in gardens in warm, humid weather. As Devon said, more photos of the gills and of a split mushroom will aid in identification. The spore prints of this group are jet black. To obtain a spore print, remove the cap from a mature mushroom, lay it on white paper, and cover with a glass jar. In 24 hours, you should have a spore print color to help with identification. Good luck (and when in doubt, throw it out).

Dorie, thanks for the 'spore print' thing. I am out of town at the moment but I did just have some shrooms pop up from where I moved the turkey pens. I'm not planning to eat them but it would be cool to find out what kind they are.

very cool thanks guys