Regarding San Martin (a winery I did a lot of business with whilst a buyer in Texas, btw):
The earthquake might have been the final straw (and oddly enough, I was there immediately after that happened), but the demise of San Martin was by that point already inevitable.
San Martin was one of the older family properties in the CA wine business, back when that valley was one of the bastions of that biz. As late as the early 1980s, San Martin was still dominated by generic jug wines, including a big business in 1.5Ls of various sherries and ports. They also had a history of producing Cold Duck and other cheap sparklers.
When the business shifted from generics to varietal wines, and from jugs to 750ml, San Martin attempted to shift as well. They managed to get a good winemaker from Germany, who pioneered the "Soft" wines that became so popular, and provided a bridge between the sweet generics and the trendy new dry wines.
But San Martin never broke past the price barrier to a point where they could make any meager profit at all without playing the "make it up in volume" game, and they were unable to do that, as sourcing good cheap fruit became harder and harder, and competing against the likes of Gallo and the other big boys became more prohibitive.
Towards the end, they were sourcing Zinfandel from Baja California and Merlot from (then unheralded and unknown) the Columbia Valley. Appellations would change with every vintage; somethimes they'd change within the same vintage.
Plus, the center of the business moved clearly to the North Coast. Nobody wanted to go to south of San Jose anymore for wine. They wanted Napa and Sonoma. Remember, Monterey was not very well known at that time, and Paso and Santa Barbara were strange words to wine purchasers outside California.
But for a while, San Martin had some nice varietal wines at good price points. They weren't the flashiest, but they were sturdy and consistent and good QPR. And my fantastical side still fondly remembers that strange and wonderful little wine they used to make from that tiny little patch of vineyard right in front of the admin building. They called it Montonico, and it tasted like a cross between sweet Sherry, Madeira, and Vin Santo. And it came in a square, medicinal looking, dark brown bottle with a really, really tacky looking bright, relfective gold metallic label with white writing on it.
Towards the end they changed hands a couple of times, but it didn't improve things. They still couldn't break out of the discount rep, and couldn't sustain themselves in the jug market either. So they folded. Another casualty of change, and of being in the wrong place.