Usgalimal, the writing on the floor.

A few kilometers from Rivona, in the Pirla village lie the Usgalimal petrogylphs or simply understood as rock bruising (craving with a sharp tool). One has to get off the main road on to a dirt track for around 2 kilometers to reach the stone floor on the banks of the Kushvati river at Usgalimal. Though the local Goan villagers knew of the rock cravings for years, it was only formally discovered in 1993.

The prehistoric art, according to various opinions of experts appears to be done over a period of time, dating anytime between 8000 to 2500 B. C.Carved on hard laterite stones, it is assumed that the Kush Tribe settled near the Kushavati river source, were hunters and food gatherers displaying shamanistic habits.

Spread over several square meters, around 100 such cravings including foot prints and a Triskelion (series of concentric circles) are etched in the stone river bed. In fact, most of the carvings indicate aspects of their life then, including animals, women and children.

There is no demarcation nor enclosure around the carvings, so one will have to study the laterite surface to find them. Though it is not difficult to do so. Most of the bank remains submerged during the monsoon and following months, so the best bet to see them would be summer months. It is possible to view them just prior to the onset of monsoons as I did. But be careful as the stone bank is quite slippery during this time.

Close by is a large water filled quarry, a remanent of the mining activity. Do not mistake this to be a shallow lake as tourists who are not familiar with place tend to do. Not advisable to jump in at all.
Suggested readings: http://digitalgoa.com/stone-age-carvings-in-goa/