A human foot impression on a rock
As @kwinkunks and @Gordon Stanger say, it's not possible to comment usefully on your particular observation without at least a picture and further information about the site. However, if you're asking “Is this even possible?” as a general question, the answer's yes, but under special circumstances. As an example, picture a scene in ancient East Africa: some individuals made their way across a layer of volcanic ash on the ground, leaving footprints in the process. Whether the ash was already wet or later rainfall fell on a dry ash layer (light enough not to destroy the evidence), the wet ash hardened and the footprints were buried under more ash fall - the “Laetoli” footprint tracks, discovered in Tanzania in the 1970s by Mary Leakey and her team, are remarkable evidence of bipedalism in our ancestors of ~3.7 million years ago.

References:

https://en.wikipedia.org/wiki/Laetoli

http://www.sciencedaily.com/releases/2011/07/110719194356.htm