Without methods to store and transport water, they needed daily access to fresh water. So, they camped, traveled, and hunted near water systems. In these drainages they also made, left, lost, and broke stone tools. These points washed into creeks or rivers and become part of their gravel system over the centuries.

Why are the most commonly found artifacts arrowheads?

An arrowhead or point is the usually sharpened and hardened tip of an arrow, which contributes a majority of the projectile mass and is responsible for impacting and penetrating a target, as well as to fulfill some special purposes such as signaling.

Are my arrowheads worth anything?

Since they are so common, you wont be able to sell a typical arrowhead for much. However, some arrowheads are worth much more than others. An arrowhead can be worth $20,000 in the best cases, even though it might only be worth $5, and an average arrowhead is only worth about $20.