This name is a synonym of Xanthisma grindelioides (Nutt.) D.R.Morgan & R.L.Hartm..
The record derives from TICA
(data supplied on 2012-02-11)
which reports it as a synonym (record C4C398DF-FE1C-4703-84C3-7EADDF3559CA) with original publication details: 1947.
This name record (from TICA) was not included in version 1 of The Plant List. It is possible the same name was included from a different data source, to check this you can search for Haplopappus nuttallii in version 1 of The Plant List.