How do I get the Ground type marowak on Sun and Moon?

I've currently got a level 32 Cubone and it's not evolving because it's daytime. I thought it'd be as follows:
>Evolve cubone at night
>it's the new fire/ghost type
>evolve cubone at day
>it's the Ground type

I chose Cubone because I wanted a ground type that was good, not a fucking Fire/ghost type.