Definitely a dry spring, which in that arid area means less plants. I read much of the Diablo Mountains were "barrens" in summers, like the San Joaquin Valley. There'a great history book called "California's Fading Wildflowers" by Minnich (UC Riverside). He went back and re-translated the Spanish explorer and other accounts from the mission period.
Fascinating to read, from the LA Times "flower reports" (folks used to spend their weekend days in the hills picnicking with the wildflowers before it was all developed) to the explorers not finding any natives in the Livermore valley (must have been too arid).
I dig these types of recent history books, like Cadillac Desert (at least the first part).