Every autumn, hundreds of thousands of mule deer, elk, pronghorn and moose move down from the high country of the American West to find food and survive the winter. Every spring, they make the trip back. This map shows where they go — built from the GPS collar tracks of 4,952 individual animals followed by USGS scientists and state wildlife biologists, across 173 herd units in 10 western states between 1999 and 2024.

Use the controls below to filter by species, by state, or by feature type. Click any shape on the map to see who uses it, when it was tracked, and how heavily it’s used. Or pick one of the featured corridors lower down on the page to load that herd’s actual GPS migration tracks onto the map.

What you’re looking at

The coloured areas on this map aren’t guesses or generalisations. Each one is the output of a statistical model fed by hundreds — sometimes thousands — of GPS fixes from individual collared animals. When biologists put a tracking collar on a mule deer or elk and follow it for several years, they capture the exact path that animal walks between summer range and winter range. Stack the tracks from 50 or 100 animals in the same herd on top of each other and a corridor emerges: a defined ribbon of habitat that the herd actually uses, year after year.

Two ideas matter here. First, these corridors are traditional. Big-game migrations are learned behaviour, passed from mother to fawn or calf. Researchers have shown that mule deer follow the green-up of spring vegetation up the mountain almost to the day, and that they rely on the same stopover meadows their grandmothers used. Second, the corridors are narrow. The Sublette mule deer migration in Wyoming covers 150 miles — but most of those miles squeeze through habitat bottlenecks just a few miles wide. Lose one of those bottlenecks to a subdivision, a highway, or a poorly placed fence, and the whole migration is at risk.

How to read the map

Every shape on the map is one of four feature types. Click the legend chips in the controls bar to toggle each on and off.

• Migration corridors — the routes animals use to travel between seasonal ranges. The colour ramp from pale yellow to deep red shows the share of the tracked herd that uses each part of the corridor. Yellow areas are the outer envelope; red areas are the core route that nearly every animal in the herd passes through.
• Stopovers (purple) are critical rest and refuel sites along the corridor. Animals pause here for days or weeks during the journey, putting on the body fat they need to keep moving. Lose a stopover and animals run out of energy before they finish the migration. These are some of the highest-value conservation targets on the entire map.
• Winter range (blue) is the lower-elevation, snow-free habitat where herds concentrate from late autumn through spring. Most winter mortality — from starvation, predation, vehicle strikes — happens here.
• Year-round range (teal outline) is mapped where biologists have data showing the herd uses the same area in every season, rather than migrating between distinct summer and winter ranges.

Use-class labels like Low use, Medium use, High use and Very high use describe the share of the tracked herd that uses each polygon — not how many animals are present at a given moment, but how many individuals showed up there over the years of tracking. Stopover is its own category, defined by repeated, sustained use rather than transit.

Why big-game migrations matter

The largest land migrations remaining in the contiguous United States are the long-distance moves of mule deer, elk and pronghorn through the Greater Yellowstone Ecosystem, the Wyoming Range, the Red Desert, and the great basin and range country of Nevada and Utah. Pronghorn complete one of the longest annual land migrations of any North American mammal — rivalled only by caribou in the Arctic. These migrations are not optional behaviour. They are the strategy that lets a 200-pound ungulate survive in a landscape where the snow line moves 4,000 feet vertically between seasons.

Migration corridors also have an outsized effect on regional ecology. A herd of 5,000 elk moving along a corridor distributes seeds, fertilises grasslands, prunes shrubs, and feeds wolves, mountain lions, bears, eagles and ravens. Stopovers become local biodiversity hotspots. The corridors and stopovers don’t just keep big game alive — they sustain entire food webs.

And they sustain human economies. Mule deer hunting alone generates hundreds of millions of dollars a year across the western states. Wildlife watching brings tourism revenue to gateway communities. Healthy big-game populations are a cultural and economic pillar of the Mountain West, and they all depend on these narrow ribbons of habitat staying connected.

The five species mapped here

Mule deer — the long-distance specialists

Mule deer (Odocoileus hemionus) are the headline species of the western US migration story. They’re the most-tracked animal in this dataset, with 86 herd units spanning every state in the western migration corridor network, and the longest documented routes — including the famous 150-mile Sublette herd migration through the Red Desert to Hoback Basin in Wyoming. Mule deer migrations are also the most fragile: the species has declined across much of its range since the 1990s, and biologists trace much of the decline to habitat loss along the corridors. Explore every mapped mule deer migration on the dedicated Mule Deer Migration Map.

Elk — the high-country travellers

Elk (Cervus canadensis) move shorter distances than mule deer but in larger herds, often over more extreme elevation differences. The Jackson Elk Herd in Wyoming — which winters on the National Elk Refuge in the Tetons by the thousands — is the most-photographed elk population in North America, and one of the most intensively tracked. This dataset includes 27 elk herd units, primarily in Wyoming, Oregon, Washington and Arizona, with summer-to-winter elevation drops of up to 6,000 feet. See the Elk Migration Map for the full set.

Pronghorn — the speedsters of the sage

Pronghorn (Antilocapra americana) have the longest documented annual land migration of any mammal in the lower 48 — the so-called Path of the Pronghorn, where animals from Grand Teton National Park travel more than 150 miles each way through Wyoming’s Sublette and Sublette-bordering ranges. Pronghorn can’t jump fences — they have to crawl under them — which makes them uniquely vulnerable to even minor fencing changes along their corridors. 16 pronghorn herd units are mapped here, from the high sagebrush country of Nevada and Oregon to the desert grasslands of Arizona and New Mexico. See the Pronghorn Migration Map for the complete picture.

Moose — the deep-snow generalists

Western moose (Alces alces) make shorter, more variable movements than the other ungulates in this dataset. Three moose herds are tracked here — all in Wyoming’s Jackson and Sublette regions — with 88 collared animals over twenty years. Because moose corridor polygons haven’t been published by the USGS team yet, selecting the Moose filter shows the actual GPS tracks instead of summary polygons. The result is a fascinating, looping pattern of riparian and willow-bottom use through the lodgepole and aspen country of the Greater Yellowstone Ecosystem. The Moose Migration Map walks through what the tracks reveal.

White-tailed deer — the eastern edge of the migration map

One white-tailed deer herd is included — the Selkirk herd of northeast Washington, which makes a short but distinct seasonal move between higher-elevation summer range and lower-elevation winter range along the Pend Oreille River. White-tailed deer don’t typically make the dramatic long-distance migrations of mule deer or elk, but the Selkirk herd is an exception that’s well worth seeing on the map. The White-tailed Deer Migration Map covers the data in detail.

Big-game migrations by state

The data behind this map covers ten western states. Each state has its own collection of herd units, its own state wildlife agency tracking program, and its own local conservation challenges. The state pages below show every mapped corridor and stopover in that state, plus state-specific stats and the major herds to know about.

• Wyoming — the migration capital of North America. Home to the Sublette mule deer migration, the Path of the Pronghorn, the Jackson Elk Herd, and dozens of other tracked herds. WY contributes more mapped corridor area than any other state.
• Utah — 13 mule deer herds with rich herd-size and acreage data, from the Beaver and Boulder ranges in the south to the North Slope of the Uintas.
• Colorado — iconic herds including the White River mule deer (the largest mule deer herd in the country) and the long-distance Middle Park and North Park migrations.
• Oregon — 21 mule deer herds across the Cascades, Steens Mountain, the Wallowas and the Klamath Basin, plus pronghorn herds shared with Nevada and California.
• Nevada — mule deer making some of the most dramatic alpine-to-sagebrush elevation changes in the West, including the Ruby Mountains and the Toiyabe Range herds.
• Arizona — including the historic Kaibab mule deer herd (the population that prompted Aldo Leopold’s landmark conservation writing) plus elk migrations across I-40 and I-17.
• New Mexico — herds across the Jemez and Mt Taylor country, including several mapped in partnership with Pueblo and Tribal wildlife agencies.
• California — 27 mule deer herds across the Sierra Nevada, the Modoc Plateau, the Mendocino Range and the Klamath country.
• Washington — mule deer and elk herds across the Cascades, the Methow, the Chelan and the Selkirks (plus the state’s one mapped white-tailed deer herd).
• Idaho — cross-border elk herds shared with Nevada, including the Bruneau-Diamond Desert and Owyhee Desert populations.

Famous migration corridors to know

A few migrations have become emblematic of what these corridors look like and why they matter. Each of the herds below has its own dedicated page with full GPS track animation, herd history, and conservation context.

The Sublette Mule Deer (Red Desert to Hoback)

The most famous big-game migration in North America. Mule deer travel up to 150 miles between summer range in the Wyoming Range and winter range in the Red Desert — the longest documented mule deer migration anywhere, mapped from 377 collared animals tracked between 2010 and 2024. The corridor passes under highways through specially built wildlife overcrossings and underpasses, and was designated as Wyoming’s first official migration corridor in 2008. Read the full story on the Sublette Mule Deer page.

Path of the Pronghorn

Pronghorn from Grand Teton National Park travelling 150 miles south to winter in the Sublette region of Wyoming — a route that has been used continuously for more than 6,000 years, predating the Pyramids of Giza. The corridor is now protected through a partnership of federal land agencies, conservation groups and the Wyoming Game and Fish Department. See Path of the Pronghorn for the full GPS track playback.

The Jackson Elk Herd

One of the largest concentrations of elk anywhere on Earth winters on the National Elk Refuge just outside Jackson, Wyoming. The herd’s 11,000-plus animals migrate seasonally up into Grand Teton National Park and the Bridger-Teton National Forest each spring, returning in the autumn snows. 650 GPS-collared individuals have been tracked here. See the Jackson Elk Herd page.

Kaibab Mule Deer

The most-written-about deer herd in conservation history — the population that informed Aldo Leopold’s A Sand County Almanac after a 1920s management disaster wiped out predators and led to a deer-population crash. Modern GPS tracking shows the surviving herd migrating off the North Rim of the Grand Canyon to lower-elevation winter range each autumn. See the Kaibab Mule Deer page.

Ruby Mountains Mule Deer

Northeast Nevada’s Ruby Mountains rise 11,000 feet straight out of the sagebrush, and the mule deer there make one of the most dramatic elevation migrations of any tracked herd — from alpine cirques in summer down to the Humboldt River valley in winter, with elevation drops of 6,000 feet over just 20 miles. See the Ruby Mountains Mule Deer page.

Sheldon-Hart Mountain Pronghorn

Pronghorn moving between the Sheldon and Hart Mountain National Wildlife Refuges — a transboundary migration across the Nevada-Oregon line through some of the most remote sagebrush country in the lower 48. See the Sheldon-Hart Pronghorn page.

Wyoming Range Mule Deer

A long-distance mule deer migration through the Wyoming Range from Hoback Basin to Pinedale, recently in steep decline due to a series of severe winters and concern about coal-bed methane development along the corridor. See the Wyoming Range Mule Deer page.

Wind River Mule Deer

The Wind River Range mule deer corridor is one of the longest-running tracking studies in the Greater Yellowstone Ecosystem, with continuous GPS data going back to the early 2000s. See the Wind River Mule Deer page.

The data behind this map

Every shape on this map comes from the USGS Corridor Mapping Team, working in partnership with state wildlife agencies, Tribal wildlife departments, university researchers, and federal land management agencies. The underlying data — 14,774 GPS migration tracks from 4,952 individual collared animals — was collected by capturing animals (typically by helicopter net-gunning in winter), fitting them with GPS satellite collars, and following each animal for two to seven years.

Researchers then use a statistical technique called a Brownian bridge movement model to turn each animal’s GPS points into a continuous movement path, account for the time between fixes, and estimate the probability of the animal having been in any given location along the route. Stack those probability surfaces across all the animals in a herd, and you get the corridor and stopover polygons you see on this map.

The result is the most rigorous, evidence-based view of big-game movement ever assembled for the American West. It’s also unusually transparent: every herd polygon comes with metadata about how many animals were tracked, how many years of data went into it, and what statistical thresholds were used.

The data is published openly under a USGS public-domain licence. It is updated periodically — this map reflects the December 2024 USGS release.

Threats to migration corridors

The biggest threats to big-game migrations in the West are not the things that kill individual animals; they’re the things that fragment the corridor itself. Once a herd loses its corridor — or even loses one critical bottleneck within it — the migration can collapse within a generation, and decades of conservation work can be undone.

• Energy development — oil, gas, wind and solar infrastructure across the Red Desert, the Wyoming Range, and the basin-and-range country of Nevada. Well pads and turbine arrays don’t just take up space; they create roads, traffic and disturbance that animals avoid.
• Roads and highways — not just direct vehicle strikes (which cause tens of thousands of mule deer deaths a year across the West) but the barrier effect of busy roads animals refuse to cross. Wildlife overpasses and underpasses, increasingly funded as part of state DOT projects, are some of the most cost-effective conservation interventions ever measured.
• Fences — especially the wrong kind. Tall, woven-wire sheep fences are nearly impassable to pronghorn (which can’t jump) and dangerous to mule deer fawns. Wildlife-friendly fence standards now exist, and replacement programs are underway across Wyoming, Idaho and Nevada.
• Subdivision and exurban development — particularly in winter range, where private land at the foot of public-land summer range gets bought up and developed faster than it can be conserved.
• Severe winters and prolonged drought — climate-driven extremes that have hit the Wyoming Range mule deer, the Sublette herd, and several Colorado herds hard in recent years.

Frequently asked questions

Are these maps showing live tracking?

No. The polygons and tracks are statistical summaries built from years of historic GPS data. Live animal tracking is occasionally published by state agencies for research outreach, but isn’t shown here. If a state agency releases real-time tracking we’ll add it as an overlay.

Why aren’t moose corridors mapped?

Moose tend to move in less directional, more home-range-like patterns than deer or pronghorn, so the USGS team hasn’t produced corridor polygons for them. The actual GPS tracks for the three tracked Wyoming moose herds are shown when you select the Moose filter — they give a strong sense of where these animals spend their time even without a smoothed corridor polygon.

Can I use these maps for hunting planning?

These maps are excellent for understanding where the herds are, when they’re moving, and which areas they depend on. They are not a substitute for state hunting unit maps, public-land boundary maps, or current-year season information from your state wildlife agency. Combine this map with your state’s GMU (Game Management Unit) map and you’ll have a much clearer picture of how a herd uses its range.

Why don’t I see any corridors in my state?

The dataset covers ten western states (AZ, CA, CO, ID, NM, NV, OR, UT, WA, WY). Migration corridor mapping is an active area of research and several more states are working on similar datasets — we’ll add them as USGS publishes them. Montana in particular has substantial work underway.

Can I download the data?

Yes. The full USGS dataset is freely available at apps.usgs.gov/western-migrations, where you can download per-herd shapefiles, view the underlying study reports, and read the methodology in detail.

What’s the difference between “corridor” and “winter range”?

A corridor is a route — the path the herd takes between seasonal ranges. Winter range is a destination — the area the herd lives in once it arrives. Both can be on the same map for the same herd, and both are critical conservation targets, but they protect different parts of the annual cycle.

Why are some corridors mapped from just a few animals?

Sample sizes vary widely — from a handful of animals in some Nevada and Arizona herds to several hundred in Wyoming’s Sublette and Wyoming Range herds. The USGS team flags low-confidence corridors with metadata so users can judge how robust a given polygon is. Click any feature on the map for the herd-level stats, including the number of tracked animals and years of data.

I work in conservation — can I use these maps in my reports?

Yes. The data is in the public domain (USGS work product). Standard practice is to cite the USGS Corridor Mapping Team and the relevant state wildlife agency partners; full citation details are on the USGS portal.

About this map

This interactive map was built by MapScaping using open data from the USGS Western Migrations initiative, the Wyoming Game and Fish Department, the Utah Division of Wildlife Resources, and the other state wildlife agencies whose collar data underpins the dataset. The map is updated when new USGS data releases become available. If you spot a problem with the map or want to suggest an improvement, drop us a line.