San Bernardino county California family

In the Pioneer Cemetery of San Bernardino co. CA is the grave of one William D. Duty, d. 7 Dec 1915, no age or birth date given. Who is this person? The only Duty family that seems to be in this county around this time is that of Edwin and Aria (James) Duty, so one might think this could be an infant son of theirs. But he does not appear in their household in the 1910 census (in neighboring Kern co.), so if so, theoretically should be born after that census; and he doesn't appear in the California Birth Index, which begins in 1905. This family apparently was in San Bernardino co. at least between 1912, when son Kenneth was born there, and 1916, when father Edwin died there; though during the preceding years they were in Kern co. mostly. Anybody have any ideas?