I am not related to this line of Yager's but I think this is your Robert. Sorry i have no information to offer, but it will give you enough to further your search. The 1940 census states that Robert Yager was a truck driver in road construction. Could be he constructed roads for the coal mines.
Robert Yager in the 1940 Census
Age 47, born abt 1893
Birthplace Michigan
Gender Male
Race White
Home in 1940
610 Thirteenth Street
Golden,
Jefferson, Colorado
Household Members Age
Head Robert Yager 47
Wife Minnie Yager 48
Daughter Beatrice Yager 14
Daughter Alice Yager 13
Daughter Gracie Yager 9
Daughter Goldie May Yager 3
Son Robert Yager 20