Oh well; I’m not too motivated to correct AP.
From a 2015 article:
Moab resident Louis[e] Williams, who has researched the life of William Granstaff, says her study shows he never went by the moniker 'Bill', and likely also spelled his surname with a 'd' after the 'n'.She is calling for the landmark to be renamed Grandstaff Canyon, as she believes this would be the most historically accurate version.
Speaking about the current name, she added: 'I don't know anybody who would die and want their name to be left like that.'