Relatives of the Kidder family, who are largely credited as the first family of the Nevada County Narrow Gauge Railroad in the Grass Valley area, are gathering today to honor that branch of their family tree. John and Mia Renshaw and their family will host their private annual gathering today at the Nevada County Narrow Gauge Railroad Museum. John Flint Kidder, a New Yorker and civil engineer, superintended construction of the Narrow Gauge Railroad between 1875-76, said Ron Kapper, secretary of the museum. “It was the lifeline for this county,” Kapper said, noting the train made possible travel to Colfax, …