Colorado GMU 21 Mule Deer Hunting
Rio Blanco and Garfield counties, northwest Colorado · 888 sq mi
Based on the EASIEST unit-wide buck or either-sex hunt code available to adult Colorado residents in the 2026 primary draw — the lowest preference-point tier that drew reliably. Private-land-only and Ranching for Wildlife hunts are excluded because neither is a unit-wide public-land opportunity — NOT because the public cannot draw them. A private-land-only license requires the hunter's own permission to hunt private ground; a Ranching for Wildlife license is valid on the participating ranches enrolled in that program. They are separate systems. Other weapons, seasons and nonresident applicants can require substantially more points. The band is a floor, not a target: even the easiest qualifying hunt here sits in that range.
What hunting GMU 21 is like
Colorado GMU 21, straddling Rio Blanco and Garfield counties in the northwest region, spans 888 square miles of rolling to moderately steep terrain. Elevations range from 5,100 feet to 9,100 feet, with typical terrain at 6,500 feet. Thirty-four percent of the unit is gentle, 48 percent moderate, and 18 percent steep or rugged. The landscape supports mule deer across a wide elevation band, making it accessible for hunters working multiple seasons across fall months.
About 87 percent of the unit, roughly 776 square miles, is generally open to public hunting on BLM and State Wildlife Areas. The remaining land is predominantly private (12 percent), with small state trust holdings. This ownership pattern means the majority of the unit is available to the public, though access to specific holdings depends on roads, trailheads, and private inholdings within the BLM parcels.
Mule deer occupy winter ground—marked by a Winter Concentration layer covering 51 percent of the unit—through the early part of the fall hunt. Summer Range covers only 26 percent of the unit, while Migration Corridors span 19 percent, indicating that much of the deer population congregates on winter ground or moves through predictable routes as the season progresses. The overall seasonal pattern shows deer shifting toward winter concentration areas as autumn advances, though timing and extent vary with weather and snow.
The unit offers four seasons for mule deer bucks: archery from September 2 to September 30; muzzleloader from September 12 to September 20; a second rifle season from October 24 to November 1; and a third rifle season from November 7 to November 15. Early seasons occur during velvet shed and early fall transition; the rifle seasons span early fall migration and the pre-rut and rut phases. Draw difficulty for the easiest unit-wide buck code available to adult Colorado residents is Moderate, requiring 1–2 preference points. Hunter pressure across the unit is low overall. The draw includes at least one premium buck season requiring substantially more points than the standard qualifying hunts.
Terrain & elevation
- Elevation
- 5,100–9,100 ft, typically around 6,500 ft
- Steepness
- Steep — mean slope 15.6°
- Slope breakdown
- 34% gentle · 48% moderate · 17% steep · 1% rugged
- Ground you can count on
- ~776 sq mi, plus ~1 sq mi of State Trust Land where access depends on enrollment
Land & access
About 87% of GMU 21 is public land a hunter can count on — BLM and State Wildlife Areas.
- BLM87%
- State Wildlife Area<1%
- State Trust Land<1%
- Private12%
Where mule deer live in the unit
Colorado Parks & Wildlife maps mule deer seasonal ranges statewide. This is how much of GMU 21 each range covers — the single best clue to whether mule deer are here in September, in November, or only passing through. The layers overlap, so they do not add to 100%.
- Overall Range100%the full extent of range CPW maps for mule deer — near 100% on most units, and not a statement about when mule deer are present
- Winter Range81%used in winter
- Winter Concentration51%where mule deer bunch up in winter
- Summer Range26%used in summer
- Migration Corridors19%movement between ranges, not residence
Mule Deer seasons & weapons (2026)
| Season | Dates | Tags offered |
|---|---|---|
| Archery | September 2 – September 30 | Buck |
| Muzzleloader | September 12 – September 20 | Buck |
| 2nd Rifle | October 24 – November 1 | Buck |
| 3rd Rifle | November 7 – November 15 | Buck |
Dates span every hunt code of that type in this unit and can differ by code. Confirm the current brochure with Colorado Parks & Wildlife before applying.
Fall weather
- September — highs around 75°F, lows around 46°F (mid-elevation normals)
- October — highs around 61°F, lows around 35°F, about 0.7 in of snow (mid-elevation normals)
- November — highs around 46°F, lows around 24°F, about 1.6 in of snow (mid-elevation normals)
GMU 21 mule deer hunting FAQ
Can a hunter with zero or one preference point realistically draw a tag in this unit?
Yes, for the easiest unit-wide buck hunt codes. The Moderate draw difficulty indicates that an adult Colorado resident applying for the lowest preference-point tier that drew reliably in recent primary draws can expect to succeed at 1–2 points on those hunts. Other seasons, weapons, and nonresident applicants face substantially higher requirements, and the unit holds at least one premium buck season requiring far more points.
Which seasons are best for hunters who prefer milder weather?
Archery and muzzleloader both fall in early September, when mid-elevation temperatures average highs around 75 degrees Fahrenheit and lows near 46 degrees. By mid-October, highs drop to 61 degrees; November temperatures average highs around 46 degrees with snowfall increasing to 1.6 inches per month, making early-season hunts significantly warmer and drier.
When should a hunter expect deer to be concentrated on winter ground?
Winter Concentration covers 51 percent of the unit, and concentrations typically build as the season advances into late fall and early winter. The third rifle season, which runs November 7–15, falls during the early pre-rut and primary rut phases when deer are increasingly active and visible. However, timing and extent of movement toward winter ground vary with weather and snow, and specific location of concentrated ground requires scouting.
What percentage of the unit can a hunter actually access for hunting?
Approximately 87 percent of GMU 21 is generally open to public hunting on BLM and State Wildlife Areas. However, access to specific parcels depends on available roads, trailheads, and whether private inholdings block entry to mapped public ground. A hunter should verify specific approach routes and seasonal closures before planning a trip.
How does the terrain affect the difficulty of hunting this unit on foot?
The unit is rolling to moderately steep, with 34 percent gentle ground, 48 percent moderate, and 18 percent steep or rugged terrain. Elevations span from 5,100 to 9,100 feet, so terrain difficulty varies by location and season. A hunter can find more manageable grades on the gentle and moderate slopes, especially in the lower and middle elevations, though reaching certain patches of public ground may require crossing steeper terrain.
Is this unit realistic for a late-season hunt during the rut?
Yes, the third rifle season runs November 7–15, which coincides with the early pre-rut and primary rut phases when mule deer are increasingly active and moving across the unit. Winter Concentration covers 51 percent of the unit, and concentrations become more pronounced as fall progresses, providing late-season hunters with predictable focal areas where deer congregate, though success still depends on snow, weather, and scouting.
Data sources & methodology
- Colorado Parks & Wildlife — Big Game hunting — seasons, weapons, hunt codes and license types
- CPW — Primary Draw rules — how preference points and the hybrid draw work
- CPW — Deer statistics, draw recap and Drawn Out At reports — the point levels behind the draw-difficulty bands
- CPW — Secondary Draw — licenses remaining after the primary draw
- CPW — Maps and GIS (Species Activity Mapping) — mule deer seasonal range
- CPW — State Trust Land Finder — which State Trust acreage is enrolled and open to public hunting
- Federal and state land-ownership datasets — land ownership and access
- NOAA climate normals — fall weather
Draw difficulty is a qualitative band, not published odds — the note under the summary above states exactly which hunt code it describes. Land shares are separate, non-overlapping categories: publicly owned is not the same as open to hunting, and State Trust Land is huntable only where CPW has enrolled it. Unit data last updated August 31, 2026.