Welcome to Coin Community, nikkinoodle.
Morgan dollars were shipped from the Mint in $1000 bags, and as those bags (over 60lbs each) got tossed around, coins clanged against each other inside. This mark is what happens when the edge of one coin hits the face of another with that kind of weight behind it - the reeding gouges into the other. Here, the striking coin came from the direction of the 8 in the date, and gouged towards the rim, leaving those classic triangular cuts.