Griffin, my 18-month-old, recently starting exclaiming “wheee” every time his stroller passes over those Matterhorn-like peaks buckling our city’s sidewalks. His urbanization, in other words, is all but complete. Which is why we’ve taken to penciling in Nursery Nature Walks–guided tours through 75 of L.A. and Ventura counties’ pastoral nooks and crannies. A not-for-profit program hatched in 1985 by Harriet Bennish, an L.A. mother aching for some leafy distraction for her child, Nursery Nature Walks are slow and deliberate, with plenty of pauses for kids to touch trees or behold the aerodynamics of butterflies. (Parent and child also learn that “nature” can be sequestered in the most unlikely spots, such as the refinery-shadowed Madrona Marsh or the Kenneth Hahn Park, near the oil derricks…