Thank you for replying, Jeff. I tried to add the .shp file to my "My Content" area so I could choose it when doing the add to my ArcGIS map, but I receive the message below saying it is not supported. I don't see any other way to select the .shp file when doing an add to the ArcGIS file. Suggestions?
This file type 'lac_trails.shp' is not supported.
ArcGIS Online supports ArcGIS map files (mxd, nmf, 3dd, sxd, ncfg, mpk, wmpk and pmf), ArcGIS layer files (lyr, lpk, and nmc), ArcGIS tools (eaz, and esriaddin), Map Templates (zip) and Desktop Application Templates (zip)