Question: I'm trying to figure out the correct formatting for multiple supers for the intro of my film. I imagine four separate superimposed lines, one appears, then fades away, until they are finished. How do I indicate this in the screenplay? Do I write each one individually, like so?

`SUPERIMPOSE: YELLOWSTONE NATIONAL PARK
SUPERIMPOSE: GRANITE PEAK
SUPERIMPOSE: 2048`

Or do I put it all under one superimpose? If so, are there commas or hyphens?

Answer: 
Just write what you mean clearly and expect intelligent people to understand it. In a recent script I indicated I wanted various lines spoken while they appeared as text on the screen. I wrote that. It was clearly signposted. People understand it.

Don't use abbreviations before you explain them. For example, above you say 'multiple supers' and I didn't know what you were referring to.

Consider including an illustration of what you mean. You can even do what I did and include a sample when you want something as simple as what you seem to be saying you desire. Create it using freely available software in low definition if necessary and point out how what you want differs from what you provided.
I'm not sure it's in your best interest to specify that the movie should use multiple supers. Remember, a screenplay is just the blueprint for a movie. You only need to include the details the rest of the crew need to agree on to tell the story. Everything else can and should be left to the director and the rest of the filmmakers so that the final movie is the collaborative result of many people's creativity.

From this principle, you rarely specify how scenes should be shot, exactly how characters are dressed, or what music should be playing. Along the same lines, you can trust your fellow filmmakers to decide the best way to format your super. The only exception is if you have a strong justification for why showing each super one at a time is essential to the story, but it is exceedingly rare for a story to paint the medium to that degree.