The Sun's rays strike Earth's surface most directly at the Equator. Near the poles, the Sun's rays strike the surface at a slant. This spreads the rays over a wide area. High desert regions typically have the greatest diurnal-temperature variations, while low-lying humid areas typically have the least. This explains why an area like the Snake River Plain can have high temperatures of 38 °C (100 °F) during a summer day, and then have lows of 5–10 °C (41–50 °F).