Possibly an inky cap, but that's a very rough guess since there's no way to judge the mushroom's size from your picture. For a good identification, it's also essential to see a picture of the stem and the underside of the cap, along with a ruler for size/scale.

Take a look at the inky cap mushroom - 4th picture down- in the pub below. These are quite common and often found in landscape mulch. 

Mushrooms and Other Nuisance Fungi, http://ipm.ucanr.edu/PMG/PESTNOTES/pn74100.html