After a difficult winter of drought, beef recalls and slaughterhouse closures, West Marin’s ranchers finally have some news to celebrate. Marin Sun Farms CEO David Evans is purchasing the embattled Petaluma slaughterhouse facility that centered in Rancho Feeding Corporation’s massive recall of 8.7 million pounds of meat earlier this month. The move by Mr. Evans, a fourth-generation rancher who pioneered grass-fed beef when he founded the company in 1998, coincided with an announcement that he…