Warning: The picture below might give the answer away.
Although not the actual ones that she saw, these are the same type of "pear-look-alikes":
Did you guess the fruit of the California Buckeye (Aesculus californica)?
These large, pear-shaped leathery capsules split to reveal a beautiful, shiny, swirled-with-brown-patterned seed:
Today we were walking at Crane Creek Regional Park (in Santa Rosa), and while stopping to admire California Buckeye trees, we heard a few loud thuds as the seeds dropped to the ground. Then we noticed quite a few picnic tables under these large California Buckeye trees. It crossed our minds that it might be a risky time of year to sit at those tables (see below):
(Just kidding...no mothers were hurt in the creation of this image!)
While researching California Buckeyes, I came across a wonderful article by Roger Raiche. He did such a great job, I'm just going to direct you to Roger's article here — California Buckeye: A Tree for All Seasons. It's totally worth reading. I especially like his description of how well matched this species is to a Mediterranean-type landscape.