Customx_12 --- Welcome.
I believe it's actually L.A. County, but if you are in to panning and sluicing, you can go up to the East fork of the San Gabriel River.
The old saying, "Go where gold has been found previously" is certainly true. And if they weren't finding it, they wouldn't be there EVERY DAY including weekdays. you will however have to purchase an "Adventure Pass" to park anywhere in the canyon. I buy an Annual pass at REI every year (about $30 / yr) but as you are going up Azusa Canyon the U.S. forestry folks will be there to gladly sell you a daily pass.
Take Hwy 39 / Azusa Ave up into the San Gabriel Mountains. About 15 miles from the starting point into the mountains you will come upon the East Fork bridge --- a big steel tresle bridge. The only way you can turn is to the right (or East). Go approximately 4 miles and you'll pass the now closed down/ locked "Follows Camp". Continue on the road another 2 miles or so and you'll pass Camp Williams. There's a Cafe there if you didn't bring anything with you. Keep going for about another mile and you'll see tents / campers etc all along the road --- this is it. As I said before, they wouldn't be there every day if they weren't finding anything.
I'd be very cautious about going there this weekend though. This canyon is noted for flash flooding! That's what closed Follows Camp down --- they would spend all the money to rebuild, then wham --- hit by another flash flood. There's a good chance of rain up there this weekend. If you're adventurous (foolish) then go on up --- personally, I'd wait a week or so and give the weather time to clear up. Good luck anyway.