They drive from the redwoods to the coast where Madeleine recalls dream-like recollections of visions of her death while Scottie desperately tries to make sense of it all. The coastal scenes were filmed at Cypress Point on the 17 mile Drive near Pebble Beach and Carmel (map).
The scene was put together using location footage interspersed with studio closeups using a projected background (for optimum lighting and dialog). The closeups included a moveable tree (below, behind Scottie in a studio shot) which was also used at the location site to create seamless continuity.
Then ... The same tree is seen below in this location shot.
... and Now, in the the same view today there's an unsightly fence to keep the multitude off the rocks.
Then ... Madeleine and Scottie however are not so constrained, but stunt doubles were used for this risky scramble down the rocks.
... and Now
... and Now, The panorama below of this cove can only hint at the pristine beauty of this special part of the world when experienced in real life.
... On location ... Here's a photo taken during setup for the movie shoot. Note the 'moveable' tree and also the giant fan which tossed Madeleine's scarf around for added drama during the scene.