I would train for something next late summer/early fall. I have not run any ultras before but feel a 50K would not be much of a challenge unless it was up the side of one of the Rocky's and back down. I am current in Nashville and train on both streets and trails. I have a good 7.25 mile trail loop I run without any troubles with gain/loss to be roughly 1900 ft.
Thanks, for some reason thought maybe you were overseas (with the states vacation comment) coming here for an ultra and wanted to see if you had any questions that maybe I could help answer.
Nashville isn't too far from KC area. If you are ever looking closer to home, the Trail nerds are one of the largest trail running clubs in the Midwest. Many 50K's during the year and several of them in Kansas. None of them would be considered well known as JFK or Rocky Raccoon, etc., but some pretty good aid stations, technical trails (bridal and single track) and enjoyable races. Good luck with your surgery.