Formations tops are the depth at which a formation is found, except for the glacial drift.  In this case only, it is the bottom of the formation.  Well elevations are also found in this table

          All wells do not have data. 
     Wells that have a status of LOC (location) TP (terminated permit) or type of PW (permitted well) haven't been drilled yet or if they have, the company hasn't reported the information to us yet.
     Older wells may have data in the paper files that hasn't been entered in the computer.  Wells have been drilled since 1929, but we've only had a database since 1982.

          Explanation of Data
     there are three elevations: Kelly Bushing, GRound level, & Drilling rig Floor
     in the elevation table Ref_Tops gives a code that tells which elevation was used in picking the tops.
     Location_ID is the same as the API number
     AAPG_Cd is the formation code
     TVD is True Vertical Depth (for slant holes)
     Method Obtained is how the data was gathered.

     The following download is a zipped Microsoft Access database
last updated 9/6/2007, file size approximately 6007 KB
Download Formation Tops
If you do not have Microsoft Access, use the online database:
http://www.michigan.gov/deq/0,1607,7-135-3311_4111_4231-98518--,00.html