Salagrams can be identified as different forms of the Lord according to Their natural shape and markings. The markings are all natural, as found at the Kali-Gandaki River.
Facing us, with the nice, natural marking that makes a smile, is Sudarshan. Though you can't see it in this photo because it is on His back, this Salagram has a beautiful Sudarshan Chakra on the other side.
In the foreground is another very auspicious and highly unusual Salagram known as Padmanabha.