The Marin Agricultural Land Trust has picked up another conservation easement in its effort to protect farmland in perpetuity. Last week, the Marin County Board of Supervisors approved a grant worth half the price of a $3.4 million easement for the McIsaac Ranch, on the north bank of the Nicasio Reservoir. The nonprofit expects to close the deal in April. The 527-acre property has been leased by the McIsaac family for more than 137 years after a dairyman from Nova Scotia took a lease on the property in 1881. His great-grandson Jim McIsaac, an organic dairyman who operates outside Novato and has served on MALT’s board in the past, uses the property to graze cattle and hold heifers that are not in milk production. The McIsaacs purchased the property for $5 million last year after its former owners, the Cutter family, put it up for sale, marketing its potential as a multi-estate development. Unlike most ranches in West Marin that are zoned A60, an agricultural zoning with a minimum lot size of 60 acres, the McIsaac Ranch is zoned A40, allowing for denser development. (Hence the various residential parcels on the backside of Black Mountain.) Mr. McIssac was 5 years old when the Marin Municipal Water District flooded his family’s ranch, then 750 acres, to create the reservoir. He said it is rumored that the county established the more versatile A40 zoning as a response to taking Nicasio properties to build the reservoir. “It worked good for us,” he said of the unique zoning. “We got a better appraisal.” The ranch has been well kept by Mr. McIsaac, who rides his motorcycle across the land to pull invasives such as woolly and Italian thistles and purple starthistle. “That depth of care, love and stewardship of the land makes it really exciting to work with people like Jim,” said Jeff Stump, the director of conservation for MALT. With the addition of the McIsaac Ranch, MALT now protects 51,349 acres across Marin through its purchase of development rights. The ranch makes 26,507 of those acres contiguous.