Trouble draping with imported dwg file

Hi. I’m new to SketchUp. I have a DWG file from a survey where they mapped the contours of the land and the location of major trees. I’m trying to overlay the location of the trees on the land contours, but I can’t seem to get drape to work correctly. I’ve tried draping the flat part as a group and also tried it ungrouped (piece by piece). Any tips? I’ve uploaded the file in case that helps troubleshoot.

LandSurvey_Base.skp (3.9 MB)

LandSurvey_Base DRAPED.skp (4.0 MB)

Thank you! How did you make it work?