that is just rocks & coral,typical of the ground in south Florida.Sometimes I brought out a towel to lay on but that day I got some scuffed up elbows.With sun beating down it made controlled breathing a little difficult,may have effected the groups a bit.
That's the one thing I miss about moving away,it was a great spot where I could shoot up to 300 yds or so,there were huge boulders at the end that made a good back drop.There I was able set up different targets a do a little fire and maneuver.Sometimes if as friend went along we would load each others magazines so the guys shooting didn't know how much ammo was left,to practice magazine changing and to practice malfunction transistion from rifle to backup pistol.Can't do that at target ranges.Do a little running with your heart beating hard,it makes it hard to place a well aimed shot.
It was a great place to do just informal plinking also,skipping cans with a .22 or something.