I'm sure you didn't mean 'garden'. So you meant 'graben?'
Sorry, when you have a rift valley forming like the one in the Great Basin, horsts are blocks of crust that are pushed up and garbens are blocks that are pushed down as the crust at either margin are moving away from each other. So Death Valley is a garben where the hot stuff becomes closer to the surface. I think that the Kiabab (Sp?) Plateau is an example of a horst. Horsts and garbens are always next to each other. One goes up the other goes down and the two edges go east and west. From Google Earth, the African Great Rift Valley is the easiest to see. Rifting explains volcanos not above edge of the plate subduction zones.