There really isn't any (estimated 8% mestizo population). Go to Paraguay, Bolivia, or Peru and you will find another story, but here in Uruguay the indigenous blood is scarce. Sure there are a few mestizos, but this is an embarrassing story for Uruguay's history.
The Charrua Indians occupied the lands before the Europeans arrived to present day Uruguay and the surrounding areas. For centuries the indigenous tribes were cut down, until in 1831, the Churrua were apparently invited to a friendly meeting in Uruguay's Salsipuedes. There, they were massacred. Only four of the Charrua remained and were sent to France. Sad stuff.