Find spike trails off the loop trails leading to lakes and streams. Look for waterfalls. Waterfalls have pools that hold big fish. Waterfalls also often mean that the water above is difficult to reach. Concentrate on streams flowing into and out of lakes.
Many anglers fish lakes and ignore the productive water of the creeks.
Look at the headwaters and feeder streams. Look for contour lines that open up into a meadow. Look for springs and incoming streams. The river gets more water and can increase in size and have better water quality. Inaccessible places aren't always.