The primary thing that gives two dimensional photographs "three dimensional" depth is the angle(s) of the lighting source(es) that reveal(s) textures via the interplay between light and shadow. The amount of light, the angles relative to the subject and to the camera, the 'hardness' or 'softness', etc. are what define the 'depth' of a photo.

In the context of landscape photography one is often at the mercy of the weather and time of day. Waiting for the right light can be a painstaking process. In some cases, one might need to plan ahead for months to get the best angle of light provided by the sun on a particular scene. Then one must hope that the weather cooperates as well. If the weather isn't right today, it might be right tomorrow at the same time (give or take a few minutes) when the sun is in the same spot in the sky.

In a deep ravine the problem is compounded by the often flat lighting when everything is in shade and illuminated by diffused light from above. The limited time during the day when the sun is shining directly into the gorge, if there is such a time, can be the best or worst possible time to capture an image. It all depends on the particulars of that location.

As far as the enormity of the gorge goes, including something in the frame that people will recognize and understand to be a more or less "standard" size for that thing will help to give a sense of scale to the image.