Reas Pass is a mountain pass in Fremont County, Idaho at about 2,116 m (6,942 ft) above sea level. It sits roughly 12.5 km (7.8 mi) SSW of West Yellowstone.
Reas Pass, elevation 6,930 feet (2,110 m), is a mountain pass on the Continental Divide in Fremont County, Idaho, about 8 miles (13 km) southwest of West Yellowstone, Montana. The pass lies essentially on the Idaho-Montana border, but modern maps show that the summit lies entirely in Idaho, because the Divide and the state line do not quite coincide here. The pass is also somewhat unusual in that, despite being the lowest crossing of the Divide in the vicinity, it has evidently never been traversed by a highway of any significance. Starting in 1909, it was used by a branch line of the Union Pacific Railroad running between Ashton, Idaho and West Yellowstone; however, the line eventually became unprofitable and was closed in 1979.From the Wikipedia article “Reas Pass”, licensed under CC BY-SA 4.0.
Sunrise & sunset directions
At Reas Pass the sunrise point swings a long way through the year: about 55° (NE) at the June solstice and 123° (ESE) in late December. Sunset moves from 305° (NW) in June to 237° (WSW) in December, and the midday sun climbs to 69° in summer but only 22° in winter.
| Date | Sunrise | Azimuth | Sunset | Azimuth | Noon sun | Daylight |
|---|---|---|---|---|---|---|
| March equinox (Mar 20) | 7:29 AM | 90° E | 7:37 PM | 271° W | 45° | 12h 09m |
| June solstice (Jun 21) | 5:41 AM | 55° NE | 9:14 PM | 305° NW | 69° | 15h 34m |
| September equinox (Sep 22) | 7:13 AM | 89° E | 7:24 PM | 271° W | 46° | 12h 11m |
| December solstice (Dec 21) | 7:59 AM | 123° ESE | 4:48 PM | 237° WSW | 22° | 8h 49m |
Azimuth is measured clockwise from true north (90° = east, 270° = west). Computed for 2026; values change by less than a degree from year to year.
Golden hour & blue hour by month
Mountain passes sit above valleys, so they reward sunrise and sunset with layered ridges, valley fog and long shadows.
| Month (15th) | Blue hour starts | Sunrise | Golden hour ends | Golden hour starts | Sunset | Blue hour ends | Daylight |
|---|---|---|---|---|---|---|---|
| January | 7:26 AM | 7:59 AM | 8:45 AM | 4:25 PM | 5:11 PM | 5:43 PM | 9h 12m |
| February | 6:56 AM | 7:26 AM | 8:07 AM | 5:13 PM | 5:54 PM | 6:24 PM | 10h 28m |
| March | 7:09 AM | 7:38 AM | 8:17 AM | 6:52 PM | 7:31 PM | 8:00 PM | 11h 53m |
| April | 6:11 AM | 6:41 AM | 7:20 AM | 7:30 PM | 8:09 PM | 8:40 PM | 13h 28m |
| May | 5:24 AM | 5:58 AM | 6:40 AM | 8:04 PM | 8:46 PM | 9:20 PM | 14h 48m |
| June | 5:03 AM | 5:40 AM | 6:25 AM | 8:28 PM | 9:12 PM | 9:49 PM | 15h 32m |
| July | 5:19 AM | 5:54 AM | 6:38 AM | 8:25 PM | 9:08 PM | 9:44 PM | 15h 14m |
| August | 5:57 AM | 6:28 AM | 7:08 AM | 7:52 PM | 8:32 PM | 9:04 PM | 14h 04m |
| September | 6:35 AM | 7:04 AM | 7:43 AM | 6:59 PM | 7:37 PM | 8:07 PM | 12h 33m |
| October | 7:11 AM | 7:41 AM | 8:20 AM | 6:02 PM | 6:42 PM | 7:11 PM | 11h 01m |
| November | 6:51 AM | 7:22 AM | 8:06 AM | 4:14 PM | 4:58 PM | 5:30 PM | 9h 36m |
| December | 7:22 AM | 7:55 AM | 8:44 AM | 3:58 PM | 4:46 PM | 5:20 PM | 8h 51m |
Local time (America/Boise), including daylight saving time. Golden hour runs from about −4° to +6° solar altitude, so the morning golden hour begins during blue hour, before sunrise.
Milky Way & night sky
From Reas Pass, the Milky Way core is visible in a dark sky from March through September. June gives the longest window (about 3.5 hours on a moonless night), and the core peaks around 17° above the southern horizon. Our light-pollution model puts the sky at about Bortle 1 (excellent dark-sky site), which is excellent for astrophotography.
| Month | Core visible (15th) | Hours | Max altitude | Direction |
|---|---|---|---|---|
| January | Below 10° in darkness | — | -3° | — |
| February | Below 10° in darkness | — | 8° | — |
| March | 5:19 AM – 5:59 AM | 0.7 | 13° | SSE → SSE |
| April | 3:16 AM – 4:46 AM | 1.5 | 16° | SSE → S |
| May | 1:23 AM – 3:43 AM | 2.3 | 17° | SSE → S |
| June | 11:41 PM – 3:11 AM | 3.5 | 17° | SSE → SSW |
| July | 11:26 PM – 1:46 AM | 2.3 | 17° | S → SSW |
| August | 10:25 PM – 11:45 PM | 1.3 | 16° | SSW → SSW |
| September | 9:17 PM – 9:47 PM | 0.5 | 13° | SSW → SSW |
| October | Below 10° in darkness | — | 7° | — |
| November | Below 10° in darkness | — | -3° | — |
| December | Below 10° in darkness | — | -20° | — |
Window when the galactic core is at least 10° high during astronomical darkness on the 15th of each month. Pick nights within a few days of the new moon. Plan exact nights with the Milky Way planner.
Estimated sky darkness: 1 Bortle 1 — Excellent dark-sky site. The Milky Way casts faint shadows; zodiacal light and airglow are obvious. Modeled zenith brightness ≈ 21.93 mag/arcsec². Aurora needs roughly Kp 5.5+ to show low on the northern horizon here.
Weather & best season
Long-term NASA satellite data for this area show July as the clearest month (about 36% average cloud cover) and December as the cloudiest (75%). July is the warmest month and January the coldest, which matters for gear, snow access and how long batteries last at night.
Average cloud cover (%)
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| High °F | 32 | 33 | 54 | 69 | 79 | 86 | 96 | 94 | 87 | 76 | 58 | 37 |
| Low °F | -30 | -33 | -19 | -7 | 10 | 24 | 32 | 29 | 20 | -2 | -21 | -31 |
| Precip. (in) | 3.0 | 2.9 | 2.8 | 3.0 | 3.0 | 2.8 | 1.3 | 1.4 | 1.9 | 2.4 | 2.9 | 3.4 |
Monthly climatology for the surrounding 1° grid cell from NASA POWER (MERRA-2). Mountain sites can be colder and cloudier than the cell average.
Photography tips for this mountain pass
- Weather changes fast at elevation; carry layers even in summer.
- Summit pull-outs often face one direction; use the sun azimuth table to see whether sunrise or sunset suits the view.
- Wildflowers bloom late at pass elevations — often July to early August in the Rockies and Sierra.
- Check road status before driving: many high passes close seasonally or after storms.
- Check road and trail conditions with the managing agency before you go.
Season: Summer and early autumn are the main season; winter visits depend on plowing and avalanche conditions.
Suggested gear: Telephoto lens, Tripod, Warm layers, Road-condition app. Work out exposures with the depth of field, ND filter and NPF rule calculators.
Nearby photo spots
Other locations within 25 km of Reas Pass, closest first.
Mountain Pass
Lake
Scenic Viewpoint
Mountain PeakCampgrounds nearby (Recreation.gov)
- Big Springs Grp. Area - Island Park9.4 km (5.8 mi) · reservable
- Big Springs Warming Hut12.7 km (7.9 mi) · reservable
- Bakers Hole (Mt)13.0 km (8.1 mi) · reservable
- Flat Rock (Idaho)14.3 km (8.9 mi) · reservable
- Basin Station Cabin16.2 km (10.1 mi) · reservable
FAQ
When is the best time to photograph Reas Pass?
What time is golden hour at Reas Pass?
Where does the sun rise and set at Reas Pass?
Can you see the Milky Way from Reas Pass?
Do you need a permit to photograph at Reas Pass?
How far is Reas Pass from West Yellowstone?
Sources
Location data: Wikidata, USGS GNIS / GeoNames, Wikipedia. Sun, moon and Milky Way times are computed by LWPhoto Atlas for 2026. Climate: NASA POWER. Sky darkness is a population-based estimate (Walker's law), not a measurement. See data sources & licenses.