Then ... Having "dodged the draft" as it were, Harold drives Maude in his Jaguar-hearse to the slopes of a grass-covered open space.
... and Now, this was filmed just off Sand Hill Road near Highway 280 on the border of Menlo Park and Woodside (map). What was open space in 1971 is now the site of the Horse Park at Woodside. When CitySleuth visited this spot (2016) he was incredibly fortunate; the site was being leveled for a new barn; soon the exact matching shot would be blocked. The large foreground tree and one of the two small trees beyond it are still there.
Here's a recent aerial of the Horse Park showing the locations appearing in this scene. Location 1 is the large tree seen above, location 2 is the small tree.
Then ... Maude encourages Harold to somersault down the hill... "Everyone has the right to make an ass out of themselves"... they are alongside the large tree and we see a closer look at the small trees beyond.
... and Now, the tree with the deformed trunk has survived even though today it's in the middle of a horse riding ring - more clearly seen in the preceding aerial view.
Then ... Not to be outdone, Maude raises her arms and whoops skywards. For good measure the director extends her cry into a full-fledged Tarzan yell that echoes around the hills.
... and Now, from the same spot.
Then ... The frolicking continues as they dance alongside the side of a reservoir to the (Cat)chy strains of "If You Want To Sing Out, Sing Out".
... and Now, the reservoir is still there, location 3 in the aerial view; there's now a newer, larger, reservoir next to it (the reservoirs belong to the Menlo Park Municipal Water District). When the movie was filmed only the original reservoir and its curving access road intruded upon these slopes.
Then ... More high jinks.
... and Now, from next to the reservoirs this view looks east across San Francisco Bay.
Then ... They head out to Sand Hill Road down the access road, location 4 in the aerial above.
... and Now, Hey, there's still a yellow fire hydrant in the same spot!
Then ... The late afternoon sunlight diffusing through a lingering mist adds a sheen to Sand Hill Road (location 5 in the aerial above) in this elevated shot.
... and Now, from street level, no mist but still sheeny. The fence on the left follows the same line as the old but there's now a sign ahead announcing the entrance to the Horse Park.