How to add location to iOS calendar, when location doesn't have an address

I'm trying to create a calendar event and want to add a location for which there's no address. It's a run in the forest, and in the map application itself I can set the pin at the location I want (start area), but the address it tells is just the nearest. I want to have the location in the calendar to be the exact location, so I can find it in the forrest when I arrive. Is there I way to manually place the pin for the location in the calendar app?