But Lake Granby and it's upstream waters have very little to do with the total Colorado River Basin.
This cool website - https://txpub.usgs.gov/DSS/streamer/web/ - will show you where ALL the water comes from. Zoom into Lake Powell area and then select “Upstream Trace” in the upper right, then put the cursor on Lake Powell at the area close to the dam and click. You will see every stream and river that feeds into Powell.
Runoff into Lake Grandby is the bellwether test of all runoff throughout Colorado. Claims by feeble minded gullible idiots that Colorado has less snowpack due to glowbull warming and so runoff into the Colorado River has slowed at all is disputed by the runoff starting at the headwaters of the Colorado River.