Shoot a series if images by rotating your tripod head in a level, linear fashion with the horizon.  Put the resulting images in a folder.  Go into Photoshop > File > Automate. . . . , navigating to your folder of images.  Photoshop will automatically stitch the images together into a panorama that should be seamless if there is enough overlap.  Medium to short telephoto lenses will yield the best results, with about a 1/3 overlap of each image frame.  The panorama here was color tinted using the Hue/Saturation adjustment sliders.

© Christian Michaels