The Mannahatta project is an effort to recreate the "land of many hills" as it looked when Henry Hudson arrived almost 400 years ago. The effort is on going but maps and some aerial recreations have been published. For a good background on what the land was like read Mannahatta: An Ecological First Look at the Manhattan (PDF).
Neat New York trivia: The island of Manhattan has grown about three square miles because of human geoenigneering efforts. (Hat tip: La Cartoteca)