Hi Laura: I have 41 Martha Cushmans in the Cushman genealogy database. None married to an Amos (but I do not have husbands for some of these women, either.).
I believe your Amos L Mason, b. Aug 1824 in NY is listed in the 1900 census in Syracuse, Onendoga Co. NY, with wife, Sallie, b. 1829, also in NY. Both of their parents also b. NY, too, so that may help..He was a "carpenter and builder". A daughter named"inex" L. (spelling?) b Mar 1873, NY. single, is also in the household.
The IGI has him b. 24 Aug 1824 of Onondaga NY, with spouse Sarah Ann Harroun, married 31 Dec 1849.It shows his father as Cyrenus Mason and mother as martha Su...man. See: http://www.familysearch.org/ENG/search/frameset_search.asphttp://www.familysearch.org/ENG/search/frameset_search.asp with search for Amos Mason b. 1824.
Several otherIGI records show Martha Cushman as his mother. Each of these entries has a contact, so I suggest you write them to see if they can tell you more.