The 1930 Census is the most recent Census available to the public at this time. In April 2012 the 1940 Census will be released to the public, however, it will probably take one year to index it.
Marriage records are sealed in Utah for 100 years after the marriage date unless you're looking for your own marriage records.
The death index ends in 1958 and those records too are sealed for 100 years.
There are some other ideas about how to look up a person's death date at www.archives.utah.gov.gov/research/indexes/20842.htm
I'd look for Mary's death date first and then find her obituary. Hopefully her children will be listed in the obituary and where they were living when she died. Successful Searching!