Had the exact same problem on my 2004 Monaco La Palma last year. Had been in Salinas a month before and didn't notice the problem for a month.
I called my insurance company, CSAA, and the lady asked what date I was in Salinas. She looked it up and said the was a "severe weather event" that date in Salinas and that they would cover the damage.
Apparently the wind came up during the day and pulled the rail loose. There were about 6 thick bolts holding it in place and I was surprised it could even pull out.
Local RV repair shop fixed it for $608.
2004 Monaco La Palma 36DBD, W22, 8.1, 7.1 MPG
2000 LEXUS RX300 FWD 22MPG 4020 LBS
"May you live in interesting times."