Formula to insert value depending on previous field

I have what should be a simple formula need.

In column A, there are sites
Philadelphia
York
Pittsburg

In column B, there are last names
Smith
Jones
Williams

In Column C, I have a formulas that displays a result based on column A and B

If Column A [EQUALS EITHER] Philadelphia or York.....
Then Column C should be changed to "Eastern Pennsylvania"

ELSE..... column C should return the value displayed in column B.


Sample
Philadelphia - Smith
York - Jones
Pittsburg - Williams

I would expect Philadelphia - Smith to read 'Eastern Pennsylvania"
I would expect York - Jones to read 'Eastern Pennsylvania"
I would expect Pittsburg - Williams to read 'Williams"

I can't figure out whether there is a way to do an OR statement within the IF statement, or whether a lookup table would be best.

I knew I was overcomplicating this. This worked like a charm. Thank you!!!