A complex sentence is a sentence consisting of an independent clause and a subordinating clause. Or, to put it more simply, complex sentences involve more than just a straightforward noun + verb. Complex sentences include extra phrases added to a base sentence, but which cannot stand alone as a sentence. For example:
Published 4:00 am, Thursday, January 9, 1997. 1997-01-09 04:00:00 PDT Yosemite National Park -- Yosemite Valley is slowly drying out after what park rangers are calling the worst flood here in recorded history, leaving behind hundreds of upturned tent-cabins and acres of wrecked camping sites.
Lakes and Rivers. Very few lakes are easily accessible in Yosemite National Park. Tenaya Lake (above) is one of the easiest to get to (when the Tioga Road is open, late May or early June to sometime in November) and is quite popular for picnicking, swimming, and canoeing. You can see Tenaya Lake from Olmsted Point and as you drive past it.