Collection location: Menlo Park, San Mateo Co., California, USA [Click for map]
The date is only accurate to the month.
Orignally attempted to key out to species in Mushroom Demystified, but only got it to the genus Panaeolus. Darvin suggested Lacrymaria lacrymabunda (see comments) and after reading about it in Arora, Swiss 4 and searching for other images on the web, I am persuaded. I should note that the images in Swiss 4 are much more red. However, Darvin mentions that it gets paler when it dries and his own photos on the site show the red color. In addition, many of the photos I found on the web had the same color as this one.
I had read about this genus, but had never applied before. Thanks Darvin!