It doesn't look like either a
T. oregonense or a
T.gibbosum (Oregon white truffles) Based on this one photograph, I believe it may be
Elaphomyces granulatus or
Scleroderma cepa. If we could see the interior, that would help further identify it. What does this specimen smell like? If you cut it and examine the interior, it would help establish a more positive identification. You can refer to these links:
http://www.natruffling.org/scce.htm
http://www.natruffling.org/elgr.htm
http://www.rogersmushrooms.com/gallery/DisplayBlock~bid~12098~gid~~source~gallerydefault.asp
http://academic.evergreen.edu/projects/mushrooms/mtsm/s43.htm