1MH What does it mean?

What does "1MH" mean when it follows the well name and legal land description?

Kathy,

I'm just guessing, but I think the M stands for either Mississippian, Meramac or Marmaton Formation followed by the H for Horizontal.

I am assuming this is in an Oklahoma County and if it is what County would this be from?

Thanks,

Clint Liles