This challenge is part of Fortnite Chapter 2 Season 3 Week 7 Challenges you'll have to collect a total of 300 units of stone at Rapid’s Rest. This location isn't shown on your map, but you'll find it just east of Lazy Lake. It's located on the side of the river, and contains many canoes stranded by the currents.
Map
On either side of the river you'll find a good amount of large rocks. The challenge can be completed in a few dozens of picks, as long as you don't have to compete on the spot!
During the week following the publication of this challenge, many players will go on site to complete their challenges. The place could turn into a graveyard, so think about the more quiet Team Rumble mode to avoid trouble.
Original content by Romain "Zorg" Becquelin.