The term “zone” is ambiguous when applied to Utah, a large state that crosses multiple classifications based on its geography, climate, and timekeeping. Utah’s immense topographical variation, from high alpine mountains to low desert valleys, makes a single ecological designation impossible for the state. This article addresses the primary types of zones relevant to residents and travelers, including time, plant hardiness, and broad geographical areas.
Time Zone Designation
Utah is entirely within the Mountain Time Zone (MT). It observes Mountain Standard Time (MST) during the winter months, which is seven hours behind Coordinated Universal Time (UTC-7). The standard time zone is generally defined by the 105 degrees west longitude meridian.
The state observes Daylight Saving Time (DST), switching to Mountain Daylight Time (MDT) for the summer. This change occurs on the second Sunday in March when clocks move ahead one hour and ends on the first Sunday in November when they fall back. During DST, the time difference shifts to six hours behind Coordinated Universal Time (UTC-6). This consistent observance of DST across the entire state simplifies scheduling for commerce and travel.
USDA Plant Hardiness Range
The United States Department of Agriculture (USDA) Plant Hardiness Zone Map classifies regions based on the average annual minimum winter temperature. Utah presents a wide range of zones, reflecting the state’s diverse landscape and extreme elevations. The zones span from 4a in the coldest, high-elevation areas to 9a in the warmest southwestern corners.
The majority of home gardens fall between 5b and 7b. High mountain valleys, such as those near the Wasatch and Uinta ranges, often fall into the colder 4b to 6a zones, experiencing snowy winters and shorter growing seasons. Conversely, the far southwest around St. George has a much warmer climate, sometimes reaching zone 9a.
Elevation is the primary driver of this variability, as temperatures decrease significantly with altitude. Proximity to large water bodies, such as the Great Salt Lake, also creates microclimates that can temper winter lows in adjacent areas. Residents should use the USDA map in conjunction with their specific ZIP code to pinpoint their local zone, which is based on 30-year averages of the coldest winter temperatures. Selecting plants that can survive the lowest expected temperatures requires consulting this specific local data.
Major Geographic and Climate Zones
Utah’s climate and ecology are defined by three major physiographic regions: the Great Basin, the Colorado Plateau, and the Middle Rocky Mountains.
The Great Basin
The Great Basin, located in the western portion of the state, is characterized by a high desert environment with internal drainage. This means water does not flow to the ocean. The region features aridity, low precipitation, and high evaporation rates, leading to features like the Bonneville Salt Flats.
The Colorado Plateau
The Colorado Plateau covers the southern and eastern parts of the state, known for its layered sedimentary rock and iconic canyon country. This area experiences a steppe or semi-arid climate, with hot, dry summers and cold winters. It receives important moisture during the late summer from the North American Monsoon, and the physiography creates extreme temperature variations between day and night.
The Middle Rocky Mountains
The Middle Rocky Mountains province, including the Wasatch Range, runs through north-central Utah and is characterized by a humid climate. These high-elevation areas receive the state’s highest precipitation, primarily as heavy winter snowfall, which supplies the majority of the state’s water resources. Ecological zones here range from alpine tundra at the highest peaks to dense coniferous forests at mid-elevations.