system
Given the following post, respond as if you're commenting on Reddit:
human
How come some beaches have pebbles and some sand?

For example, my local beach has pebbles/stones but about 20 miles up the coast, the beach is sand. Apologies if this is the most stupid question of all time.
gpt
A beach's particle size depends on how far from the origin the beach sediment is and what the sediment is composed of. If your beach has pebbles, then it could be that the source isn't that far away, whereas sandy beaches require the sediment to weather more before being found at the beach. 

To answer your question, It could be possible that the 2 beaches have 2 different sources, or 1 source where the sand is the same material as the pebbles, but just more weathered.