You spot a stone and wonder if it is Ok to collect it? The answer unfortunately is that it depends. There are places where a person can collect rocks and places where a person should not collect rocks.
Rule #1. Never collect rocks in National Parks. Firstly, because our National Parks are treasures that everyone should preserve. Secondly, because it is prohibited at National Parks and you could get in trouble. There are exceptions though. There is a Park in California that allows gold panning in specific areas. Several of the National Parks in Alaska allow the collection of surface specimens by hand.
Rule #2. On public and private lands, it is good practice to check if rock collecting is allowed.
Rule #3. Never take a sample if taking that sample will disturb the site or if taking it would lessen the experience of visiting the site by the next person. Don’t collect any sample that you know someone else will miss.
There are places where rock collecting is specifically allowed. Rock collecting is allowed on BLM managed land including National Forests. The BLM manages a massive amount of land; 1/12th of the landmass of the US. Rocks, minerals, petrified wood, invertebrate fossils, and gem stones can be collected. There are limitations. Collection only is allowed for personal use. You aren’t allowed collect more than 25 pounds of petrified wood per day. And as usual, there are exceptions too. Don’t collect from inside caves, from mining claims, or archeology sites. There are a small number of properties where collecting is prohibited. Never, never, ever go into an abandoned mine to collect specimens.
Beach Combing usually is allowed. On road cuts collecting is allowed sometimes. On private property, if you are the owner, collect away! On other people’s property, check with the owner.
Riverbed landscaping gravel is mined from existing and former river beds. Sometimes the landscaping rocks are homogenous; sometimes there will be a wide variety of rocks, depending on the upstream geology. I have found some interesting samples in my landscape gravel!
Use your judgment when collecting but don’t over-think it. You can keep in mind that this planet we are on is almost entirely rock. Other than a very thin layer of topsoil and sand along with some water, the Earth is rock. In fact, Earth is estimated to be 5,972,000,000,000,000,000,000 tons of rock. That comes to 746 billion tons of rock per person on this planet right now. That is a lot of rock.