Donald J. McIsaac Jr., heir to West Marin’s golden era of dairy and cherished husband, father and friend, died on May 11 in Sparks, Nevada. He was 70 years old. Mr. McIsaac was born on August 29, 1941 to ranchers Lorraine and Donald J. McIsaac Sr. His Swiss-Italian great-grandfather had established the family’s Tocaloma dairy ranch on the banks of Lagunitas Creek in 1886, at the height of the region’s butter-producing era.

In those days, the distance to San Francisco and East Marin communities hindered the shipment of milk for domestic consumption, but record yields of butter and cheese were produced and sold by West Marin farms throughout the late nineteenth century. At that time, butter from Point Reyes ranches was so popular that local brands had their imprints forged by competing dairies in the Bay Area, all striving for lucrative contracts with San Francisco’s high-end hoteliers and fine food purveyors.

Mr. McIsaac’s lifelong friend, Dave Chrisholm, said his and Mr. McIsaac’s grandparents had met in 1919, and the families remained close ever since. As children the boys relished all the joys of life on a dairy ranch in the 1940’s and 1950’s. “We swam in the creek, walked along the water lines,” Mr. Chrisholm said. “I remember us being 4 years old and swinging out over Papermill Creek on a tire swing. I can still tear up thinking about him. That feels like it was yesterday.”

Brother Doug McIsaac said they had a lot of fun together on the ranch, raising animals for the 4-H Club and “fightin’ like cats and dogs” from time to time.

Growing up, Mr. McIsaac’s curiosity and sense of fun would sometimes get him into trouble. Once, when he became bored shoveling calf manure out of a shed at age nine, he realized he could fling the loads out the door instead of walking them over. Wondering how far he could reach, he pitched the clods farther and farther until he could hit the nearby highway—accidentally ambushing a surprised Sunday motorist.

Donald McIsaac Sr. was a member of the volunteer firefighting brigade, and Don Jr., his brothers Doug, David, Ted and Allen, and friend Dave, among others, all joined him in fighting a wildfire in Bear Valley in the late 1950’s. Together they battled the flames all afternoon and into the evening, until the fire was extinguished.

As a teenager, Mr. McIsaac enjoyed going to movies and car races in Petaluma, Santa Rosa and San Rafael. He spent weekends and summers hunting at the family’s famed deer camp until he graduated from high school. In 1960, at the age of 19, he enlisted in the Army and was shipped off to Korea, where he served for a year.

“Something happened to him over there,” Mr. Chrisholm said. When he returned, friends said that although he was the same sweetheart he had always been, something was different. But if he had been troubled by events in Asia, he never spoke of it.

Mr. McIsaac remained in Marin for most of his adult life, working as a fireman and paramedic. He met his first wife, Luella, and took her and her two children, Terry and Debbie, into the loving fold of the McIsaac clan. Soon came sons Buddy and Michael, and the family spent many happy years together hunting at the deer camp and fishing in the local waterways. Luella died from cancer in 1980, and Mr. McIsaac continued to raise all four children.

He had been a widower for six years when he met Margaret Allen in 1986 at Nave Lanes bowling alley in Novato, where Ms. Allen was working as a secretary of the bowling league. At the time he had a beard and the bluest eyes she’d ever seen. Later, he was a guest at a potluck dinner she hosted, and the two ended up talking all night. But when he asked her out before saying goodnight, she said no.

“I shut the door and then thought to myself, ‘What was I thinking?’” Ms. Allen said. The two began dating and were married in 1987.

“He was such a kind gentleman. He always was that,” she said. “He was a wonderful person who never said a bad word about anyone. We were very much in love. He was my soul mate. We never argued. You can’t imagine how good he was to me.” September 19 would have been their 25th wedding anniversary.

Mr. McIsaac had gone to work as an equipment operator for North Bay Construction, and, after retiring in 2001, he and Mrs. McIsaac moved to Nevada, where he worked as a tour operator for the JA Nugget in Sparks and at the Sands Regency in Reno. Despite the distances he traveled, Marge said he maintained the easygoing pace of the dairy farmer he was born to be. “Ranchers,” Mrs. McIsaac said, “they don’t have to be anywhere in a hurry.”

Don McIsaac Jr. is survived by brothers Doug, Dave, Ted and Allen; his loving wife, Margaret “Marge” McIsaac; children Buddy and Michael McIsaac and step-children Terry and Deborah Gray; step-children Robert Allen and Deborah Hales; eight grandchildren and seven great-grandchildren. He is predeceased by his mother, Lorrain McIsaac, father, Donald J. McIsaac Sr., and first wife, Luella McIsaac.