Create New Workbook With Separate Sheets From Data In Another Workbook

I have been tasked with creating a macro which creates a new workbook wherein each sheet contains the information for one site from the active sheet. The active sheet already has the values sorted by the site such that all information needing to be copied from the active sheet into the new workbook is together.

I.E.

ATL
ATL
ATL
ATL
CEN
CEN
JCK
JCK
etc.

There are 8 different sites on the active sheet: ATL, CEN, DAL, HAR, JAS, JCK, VIS, NOV

The macro needs to find the range for all of the data of each site and copy/paste that data into a new workbook such that ATL would have its own sheet, CEN would have its own sheet, and so on. The data ranges from A:R.

So, for example, the macro would find that the last row with ATL in the "B" column is 6095 and would then copy A2:R6095 and insert that data into the new workbook under Sheet 1.

I had some code that I had adapted to select the range for each of them, but the code loops through the entire sheet (which is 44,307 rows long) for each site making it a quite clunky and very slow step in an even longer macro. Since the data is already sorted, I know there must be a way to have the macro stop searching when it reaches data not equal to the data the row before, however, my experience with VBA is limited, and I have been unable to find a solution. Also, the data does not have to be conserved after being sent to the new workbook, if that would speed up the macro.