Along the Alpine division the cars pass through a forest of giant pines, which covers all the northern slopes of the Sierra Madre. The symmetrical branches weave a network against the background of blue sky. These hardy trees grasp the granite rocks with their gnarled roots and send a lacework of delicate fibres down the almost imperceptible fissures for nourishment. The roots of pines and oaks have penetrated the crevices to a depth of twelve to fifteen feet below the surface.