A comment below made me wonder could a planned turn off be different to a random turn off like my original answer below.
So a quick test this morning and...
if you turn it off through the button on the side when you turn it back on you will have the Discard and Save option.
Press home, navigate to the trip screen again and your ride is ready to resume, just press the start button again.
If the Garmin decides to turn itself off though the data stored before that is lost.
Old answer... Proved to be incorrect
Not without some manual steps
You will need to manually stop the ride by pressing the start/stop button, then save the ride from the options presented, before turning of the Garmin.
Then turn the Garmin back on before riding off.
You will then be able to stitch the GPS files together to make one continuous journey if you don't want your ride broken into multiple sections
If the power turns off mid ride that section of the ride is lost.
I know this because my Touring turned itself off a few weeks ago mid ride and I lost the first 5km of my ride.