Olympia originally had 5" L/40 Mk II guns.

C. 1917, her original armament (8" and 5") was removed and replaced by new 5" L/51.

If she today has the guns of the battleship Colorado, then these are similar to her WW1 guns - not the guns she had originally. Colorado had 5" L/51.

I photographed e.g. this on board - apparently a 6" gun, which she was never equipped with when in service:


But also this 5" L/40 Mk III:


I.e. today, she has a mixture of different guns, 6", 5" L/40 and 5" L/51...

Here, more photos:
USS Olympia 2017