I think that the rocky, mountainous terrain represents your life or the part of your life you are living now, with the rocks and mountains representing the obstacles you have gotten past in your life and the obstacles in life that you still have to get over.
Water in dreams often represents the emotions, so the bodies of water that you pass can represent times in your life when you have felt strong emotion or times in the future when you expect to be very emotional because of things that you expect to happen.
The huge ocean probably symbolizes an important event that you expect to happen in your future that you have, or will have, strong emotions about. (These could be good or bad emotions.) You could be somewhat afraid that you won't be able to control your emotions.
The parts of the dream where you and your horse jump in and out of the puddles signify emotional experiences that you have survived and that have made you stronger.
In general, traveling in a dream represents a journey through life. Since you are taking a horse and exploring, rather than speeding through the landscape by car or train, it's a sign that you are thinking about yourself and the meaning of your life.
You might also be interested in these pages on
Landscapes in Dreams
and
Travel Dreams