The Trout Creek Mountains are semi @-@ arid because they are in the eastern rain shadow of mountain ranges to the west . When moist air from the Pacific Ocean moves eastward over the Oregon and California coastal ranges and the Cascade Range , most precipitation falls in those mountains before reaching the Trout Creek Mountains . As a result , the average annual precipitation in the Trout Creek Mountains is only 8 to 26 inches ( 200 to 660 mm ) per year , with most areas receiving between 8 and 12 inches ( 200 and 300 mm ) annually . Much of the annual precipitation occurs between the beginning of March and the end of June . Most of the rest falls as snow during the fall and winter months . Snowpack at elevations below 6 @,@ 000 feet ( 1 @,@ 800 m ) usually melts by April ; however , at the higher elevations , snow can remain until mid @-@ June . Local flooding often occurs in the spring as the snowpack melts .