See census with his parents.

Ancestry.com has, in card catalog, a “U.S. Public Records Index”. It popped up as a possible additional reference when I used names and dates to look at the SSDI for John and Margaret, but I have to admit I don't fully understand where it comes from. But it somehow connects names, birth dates, and addresses. And it shows the same Denver address for Margaret and John.

It has the following for Margaret I Barnes:

U.S. Public Records Index, Volume 2
Margaret I Barnes
14 Aug 1916
30 S Emerson St, Denver, CO, 80209-2217

And it has the following for John L Barnes:
U.S. Public Records Index, Volume 1
John L Barnes
18 Dec 1924
[18 Dec 1923]
30 S Emerson St Apt 301, Denver, CO, 80209-2239 (1981)
[700 Broadway Ste 1123, Denver, CO, 80203-3444]

SSDI:
John Barnes, SS#523-12-9273, issued Colorado, born 18 Dec 1923, died 26 Jan 2001 in Claremont, Los Angeles, CA.

The U.S. Public Records Index also shows John Barnes at several California addresses.