The Clark County Historical Museum, 1911 Main St., has operated in Vancouver’s 1909 Carnegie Library since 1964.Susan Tissot, who has been executive director of the Clark County Historical Museum for 10.5 years, will leave in May for a job in California.Tissot will become executive director of the Humboldt Botanical Garden Foundation in Eureka, Calif.The move results from several personal and family factors coming into alignment, Tissot said Wednesday afternoon.She will join husband Brian Tissot, who left the faculty of Washington State University Vancouver to become director of Humboldt State University’s marine laboratory in Trinidad, Calif.“It’s an opportunity for my husband. Our son is graduating (from high school), and we will be empty-nesters this summer. The time is right for a big change,” she said.“I do have a personal philosophy,” Tissot continued. “I’ve been here 101/2 years. No nonprofit should have the same executive director for 20 years. You need new blood, fresh eyes. It’s a healthy move for the historical society. My successor will come in the door and take it to the next level.”Tissot was hired by the Clark County Historical Museum in September 2003 after 31/2 years as exhibits and public program coordinator at the Cowlitz County Historical Museum in Kelso.