SDCL § 43-25-30: Easements passed by transfer of real property to which they are attached.

A transfer of real property passes all easements attached thereto, and creates in favor thereof an easement to use other real property of the person whose estate is transferred, in the same manner and to the same extent as such property was obviously and permanently used by the person whose estate is transferred, for the benefit thereof, at the time when the transfer was agreed upon or completed.