The Marin Agricultural Land Trust will soon purchase the development rights to the Tunnel Hill Ranch, a 110-acre Tomales property named for the historic North Pacific Coast Railroad tunnel that runs below it. On Tuesday, Marin supervisors agreed to pay up to half the $1.1 million cost of a conservation easement to protect the ranch; the remainder will be raised by MALT through private donations. The funding comes from Measure A, a quarter-cent sales tax…