My first 2-piece General Service button with shank and gold gilt. How old?

[mr_larry]

I found this button deep in a park in San Francisco, about ten inches deep. I know nothing about buttons but tried to research it. I would appreciate any information anyone can give me.
On the reverse of the button on top are the letters "MN" and on the bottom of the reverse are the letters "NY." On both sides of the back are three stars between the initials.
I'm mostly interested in the approximate age of when this button would have been made.
Thanks for looking and happy hunting!

 

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[Capt. Brad]

The front of the button appears to be listed in Alberts as GI 98 (1875-1902). From what I can make out of the backmark, it is not one of the 5 that he has listed.

 

[mr_larry]

The front of the button appears to be listed in Alberts as GI 98 (1875-1902). From what I can make out of the backmark, it is not one of the 5 that he has listed.

Thank you for that information. I hit Google and found a link that lists the button:
http://www.ssfirearms.com/images/07 Cat/SS07131-146.pdf
In the top photo it appears to be the third button. It is listed as MB304H M.N., New York

The park where I found the button was used as a refugee camp following the 1906 earthquake. Prior to that it was an empty lot although quite close to a military installation.