Hello, Hilary.

I was unable to find a newspaper item about the Hadley-Newman marriage circa 1883. However, I did find the family in the 1885 Iowa State Census:

1885 IA State Census, Greene County, Washington Township

Hadley, Job, residence Town of Surry, age 55, Coal Miner, born England
Hadley, Jane, 45, Keeping House, born England
Hadley, Walter, 5, born England

I didn't find Job HADLEY in the WPA Iowa Gravestones Project Index.

I note that the 1885 CO State Census for Weld County includes a Thomas HADLEY from England; I wonder whether this was a relative of Job.

Another possible match I came across:
Denver [Colorado] Land Office Records, 1862-1908
Name: Job Hadley
Township/Direction: 4/North
Range/Direction: 67/West
Book: Register of Homestead Entries, 5. vols.
Type: Homestead Act
Bureau of Land Management: 6
Application #: 11059.00

I also found this match in the Colorado Department of Personnel & Administration index:

Hadley, Anne Jane
Old Age Pension
Weld County
1931-Aug-3

Have you already located Walter and his wife Jennie's headstone in Weld County, Colorado?