The West was built on opportunity, dreams and gold. In your travels, you may come across gold no one else has found. Make sure you have a pickaxe handy, or that nugget you see may be nothing but Fool's Gold.
There are many by the rivers mainly at the end of steams or behind waterfalls. You see a cavern enter it and root around your likely to find something in there. Places you went on your missions that involved going to a hard to find place will have gold also because the game designers were too lazy to make more hiding places. A lot of gold seams are just around a corner you pass by time and time again don't forget you look around that rock every now and again. High places there are a few gold seams just above your eye line but sure you've been up on top of everything and followed all those paths that seem to do nowhere. Follow this advice and you should find at least 30 of the 44 gold seams.