The Shaligrams are specifically described as fossil-stones which have taken shape in the Gandaki-river,  and are characterized by the presence of discus marks. Shaligrams are always naturally found in the river Gandaki. These also include the famous Kali-Gandaki River, Muktinath, Damodar Himal, Damodar Kunda, Devghat, etc.

Shaligrams are sacred 'shilas' or stones representing the abstract form of Lord Vishnu.  His followers, the Hindu Vaishnavas, place these stones in their puja altars for daily worship.  Just as the abstract form of Shiva is the stone ‘lingam’ that the Shaivites worship in their temples and homes, so is the ‘Shila’ of Lord Vishnu.

According to Hindu tradition, the Shaligram stone is the shelter for a small insect known as the 'vajra-keeta' that cuts through this stone and lives inside it. In actuality, however, these stones are the fossils of the common ammonite that lived millions of years ago when the Himalayan mountain  range formed the bed of a vast ocean floor.

Krishna, Arjuna and Bhima are said to have crossed this river on their way from India-prastha to Girivraja.
 The puranas also describe it as a sacred stream in which all the gods and titans abide (‘punyodaka surasura-nishevita’).  By merely looking at it, one would eliminate all his mental defilement, by touching it his bodily sins are burnt up,  and by sipping its water the verbal demerits are thrown out.

By worshiping Maha Vishnu in the form of shaligrama , one gains the merit of performing a thousand Rajasuya sacrifices.