What Crankin said. Going from 30 to 60 miles in one fell swoop is not a great idea for your body. Maybe if you're 25...I don't know your age, but I could never get away with it (I'll be 50 in April).
I've always read/heard the rule of thumb that you should only increase 10-15% per week. So my last five "long" rides have been something like 20, 22, 23, 26, 23, 30 miles (with a few shorter rides sprinkled in). No problems increasing like that, but I would never dream of riding 60, or even 50, yet. Next week, maybe 33-34 max for me.
Be kind to your body -- it's the only one you're likely to get.
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow