Adjusting airstrip contour

[Timber]

First off I'm new at this scenery building. Using SBuilderX313 I managed to create an airstirp using an abandon strip by the Sol Duc Hot Springs in the Olympic Mountains. Kept it very basic with a small .ini file and one summer bmp. This strip is high on one end and has a number of gullys and small mounds in it. I would like to level them off a little if that's possible. Searched for tutorials and such to see if it's possible but am unable to find any good instructions.
Here's a couple of pictures.

Google earth of abandon, was told it's at least 49 years old, airstrip by the springs.

Here's the airstrip designated WSD1

[meshman]

You can make an AirportBackgroundFlatten to match the photo area, then you can adjust the individual vertices to a height of your choosing. Flattens don't need to be flat, they can slope in many different ways.

[Timber]

Thank you Meshamn, Will work through it and hopefully level off some rank peaks and gullys.