1. Rivers: Rivers carry sediment eroded from mountains, hills, and other landforms downstream. This sediment is deposited at the river mouth where the river enters the ocean, and waves and currents distribute it along the coastline, forming beaches.

2. Erosion of Coastal Cliffs and Bluffs: Waves constantly batter coastal cliffs and bluffs, breaking them down into smaller pieces. These pieces, composed of rock, sand, and other materials, are then transported by currents and deposited along the beach.

While these are the primary sources, other factors like biological activity (e.g., shellfish creating shells) and volcanic activity can also contribute to beach sediment.