Craters of the Moon, Idaho: The Volcanic Landscape NASA Used to Train Apollo Astronauts — and Why It Still Feels Like Another Planet Today

Walk a 15,000-year-old lava field, crawl through ancient lava tubes, and stand on the same volcanic terrain where Apollo astronauts prepared for the Moon — your complete guide to Idaho’s most otherworldly national monument.

In the summer of 1969, before Neil Armstrong took his first steps on the Moon, NASA sent astronauts Eugene Cernan and Joe Engle to a black lava field in the middle of Idaho to practice. They wore street clothes and carried rock hammers, walking across a landscape so convincingly lunar that geologists considered it the most honest preparation available on Earth for the geological work awaiting them in space. That landscape is Craters of the Moon National Monument and Preserve — 750,000 acres of jagged basalt, cinder cones, lava tubes, and volcanic craters sitting on Idaho’s Snake River Plain, formed by eruptions that began 15,000 years ago and will almost certainly erupt again within the next 900 years. It is the only place in the continental United States where you can walk into an active volcanic rift zone, crawl through a lava tube formed by molten rock still cooling from its last flow, and understand with your whole body why the Moon looks the way it does.

The NASA Connection: Why Astronauts Came to Idaho

The story of NASA’s use of Craters of the Moon is one of the most underappreciated chapters in the entire Apollo programme. When NASA began preparing astronauts for lunar landings in the late 1960s, mission planners realised that the astronauts needed to function as field geologists — not just pilots — because the scientific value of the Moon missions depended on their ability to identify, document, and sample geological formations under time pressure and physical stress. Craters of the Moon was selected because its volcanic terrain closely mimics the Moon’s surface — both environments share basaltic rock formations, lava tubes, craters, and the kind of jagged, uneven terrain that challenges navigation and sampling technique in equivalent ways. In August 1969, astronauts spent a full day at the monument guided by geologists and volcanologists, learning to read volcanic rock formations, practice sampling technique, and navigate terrain that had no established path — the same skills that proved directly applicable when they reached the actual lunar surface weeks later. NASA’s engagement with Craters of the Moon did not end with Apollo — the monument continues to function as an active research and analogue training site for planetary scientists, with ongoing studies examining how its lava tube structures might relate to subsurface features on Mars and what its microbial communities can tell us about the possibility of life in volcanic environments elsewhere in the solar system.

The Geology: What You Are Actually Walking On

Understanding what formed Craters of the Moon transforms an intimidating black landscape into one of the most geologically legible places in North America. The entire monument sits along the Great Rift of Idaho — an 85-kilometre crack in the Earth’s crust running southeast to northwest across the Snake River Plain, and the deepest known open rift crack on Earth at 240 metres in places. The lava field is a composite of more than 60 individual lava flows, 25 cinder cones, and at least 8 eruptive fissure systems, all produced during 8 major eruptive periods that began approximately 15,000 years ago and last erupted around 2,000 years ago. The monument contains examples of nearly every variety of basaltic lava — from the smooth, ropy pahoehoe flows to the jagged, clinkery a’a lava — as well as tree molds where lava incinerated standing trees and left perfect hollow casts of their trunks in solid rock, spatter cones built by lava fountaining, and lava tubes formed when the outer surface of a flowing lava stream solidified while molten rock continued draining through the interior. Geologists predict with high confidence that the area will experience its next eruption within the next 900 years, with the most likely window being within the next 100 years — meaning Craters of the Moon is not a relic of a dead volcanic system but a dormant one that is very much still alive.

Best Duration

Recommended: 2 to 3 days. A single day is enough to drive the 7-mile Loop Road and hit the main features, but you will miss the cave trail system and any meaningful backcountry time. Two days gives you the full loop, the lava tube caves, Inferno Cone, the Great Rift overlook, and the tree molds trail at a pace that allows the landscape to actually settle. Three days is ideal for anyone wanting to add a backcountry hike into the Wilderness Area where no trails or markers exist and navigation is entirely by landmarks across the lava — an experience that makes the Apollo training story feel tangibly real when you are standing on featureless black rock trying to determine your position.

Day-by-Day Itinerary

Day 1 — Arrive and Drive the Loop Road

Craters of the Moon sits on US Highway 20/26/93 in south-central Idaho, 18 miles southwest of Arco — the nearest town with fuel and accommodation — and approximately 90 miles west of Idaho Falls. Enter the monument at the visitor centre and watch the orientation film, which provides essential geological context that transforms the subsequent landscape from confusing black rock into a comprehensible volcanic sequence. Drive the 7-mile paved Loop Road in the early afternoon, stopping at the North Crater Flow Trail first — an easy 0.4-mile interpretive trail through twisted pahoehoe lava formations with signage explaining the physical processes that created each surface texture and rock shape you are walking through. Continue to the Spatter Cones — a cluster of small, steep-sided volcanic cones built by lava fountaining during a single eruption event, where you can peer directly into the throat of each cone and see the solidified lava walls inside. End the afternoon at the Big Craters overlook where a series of collapsed lava craters of varying sizes give the most immediate sense of the volcanic scale of the monument, and the view across the surrounding lava field in late afternoon light — black basalt glinting orange and copper as the sun drops — is the visual introduction to Craters of the Moon that no photograph adequately prepares you for.

Day 2 — Inferno Cone, Lava Tube Caves and Tree Molds

Start at Inferno Cone — a steep, black cinder cone rising 165 feet from the Loop Road with a short but demanding climb that rewards at the summit with a 360-degree panoramic view of the entire monument, the surrounding lava fields, and the Pioneer Mountains rising to the north in a snow-capped line that makes the contrast between the frozen geological violence below and the calm mountain range above feel like a deliberate compositional choice by some geological artist. Collect a free cave permit from the visitor centre and spend the mid-morning on the cave trail — a cluster of accessible lava tubes including Boy Scout Cave, Beauty Cave, Indian Tunnel, and Dewdrop Cave, each with a distinctly different character produced by different cooling and drainage rates during their formation. Indian Tunnel is the largest and most accessible lava tube at Craters of the Moon — 800 feet long, 50 feet wide in its broadest section, and tall enough to walk upright through most of its length — and the experience of standing inside a tube formed by molten basalt flowing at 2,000 degrees Fahrenheit and then draining away to leave a hollow rock corridor is the single most viscerally geological moment the monument offers. In the afternoon, walk the Tree Mold Trail — a 0.7-mile path through a field of hollow rock cylinders left by trees that were engulfed by lava flows and then burned away, leaving perfect stone casts of their trunks at exact original positions, a fossilisation process so specific in its detail that individual bark textures are preserved on the interior of each mold.

Day 3 — Backcountry Wilderness and Great Rift

The Craters of the Moon Wilderness Area covers the southern half of the monument and has no maintained trails, no water sources, no shade, and no rescue infrastructure — it is navigated by compass bearing, GPS, and the kind of attentiveness that reminds you what travel felt like before paved paths and interpretive signage. Obtain a free backcountry permit from the visitor centre, carry a minimum of three litres of water per person plus emergency reserve, and hike south from the Loop Road into the wilderness, following the Great Rift crack southward — the deepest open rift crack in the world at 240 metres — through a landscape of cinder fields, pressure ridges, and lava collapses that no trail prepares you for because no trail passes through it. The King’s Bowl lava field in the southern section of the monument — a separate eruption site along the Great Rift — is accessible with a longer wilderness day and contains some of the monument’s most dramatic rift crack formations and a small maar crater filled with a seasonal lake. Return to the visitor centre by mid-afternoon and make the drive to Idaho Falls or Twin Falls for overnight accommodation, or stay at the monument campground for a final night under a genuinely dark sky — Craters of the Moon is one of the darkest sky designations in the entire Snake River Plain region and the star density on a clear night is among the finest available in the American Northwest.

Best Time to Visit

Late April through early June and September through October are the two optimal windows for visiting Craters of the Moon. Summer from July through August is the most popular season but the black basalt surface absorbs and radiates heat to a degree that makes midday ground temperatures exceed 60°C in direct sun — the monument’s temperature range runs from -37°C to 38°C across its annual cycle, and summer visitors who underestimate the heat retention of lava surfaces are regularly in difficulty. Spring visits from late April through early June deliver wildflowers growing improbably through the cracks in the basalt — over 750 plant species have adapted to the monument’s harsh volcanic substrate — moderate temperatures, and the cave ice formations in the lower cave system that persist into late spring from winter freezing. September and October bring cooler temperatures, golden light on the lava fields, dramatically reduced visitor numbers, and the most photogenic conditions of the year for the monument’s alien landscape. The Loop Road closes from November through April due to snow, and winter backcountry access on skis or snowshoes is possible with proper equipment for experienced winter travelers.

Best Food

There are no food vendors, restaurants, or cafes anywhere inside Craters of the Moon National Monument — the visitor centre has a small selection of packaged snacks and that is the complete extent of on-site food provision. The nearest food options are in Arco, 18 miles northeast on US-20 — a small town with a handful of diners and gas station food options that serve the region’s working community rather than the tourist circuit, which means the food is straightforward, the portions are generous, and the prices are the kind that remind you how affordable rural Idaho remains. For travelers camping in the monument, self-catering with a camp stove and pre-prepared food from Idaho Falls or Twin Falls supermarkets is the most practical approach — Idaho Falls is 88 miles east and has full supermarket options including Whole Foods and local co-ops where trail food, fresh produce, and camping provisions can be assembled comprehensively before the drive to the monument. Locally, the Arco area is known for basic American diner food — burgers, breakfast plates, and Idaho potato dishes in configurations ranging from competent to genuinely excellent depending on the establishment.

Best Locations Inside the Monument

Inferno Cone is the single most commanding viewpoint in the monument — its summit panorama encompasses the entire lava field, the cinder cone clusters, and the mountain backdrop in a view that contextualises the scale of the volcanic system more effectively than any ground-level trail. Indian Tunnel lava tube is the most geologically significant and experientially dramatic feature of the cave system — large enough to walk through without stooping, complex enough in its internal architecture to require a headlamp and proper orientation, and old enough that the interior walls have developed secondary mineral formations that the main cave brochure does not mention. The Spatter Cones cluster is the most photographically unique feature in the monument — the perfectly preserved volcanic throats of individual spatter cones in a row, each one a different size and internal depth, represent a type of volcanic landform rarely preserved in accessible form anywhere in the world. The Great Rift crack in the southern wilderness area is the most geologically significant feature in the entire monument — a 240-metre deep open crack in the Earth’s crust that is the source of everything you have been walking on — and reaching it requires a full backcountry day, which means almost no casual visitor ever sees it. The North Crater Flow Trail at dawn, before any other visitor arrives, when the morning light at 5,910 feet elevation is horizontal and cold and the lava surface transitions from black to deep bronze and rust in the first hour of daylight, is the monument’s finest sensory experience and the one that makes the Apollo astronaut training story feel not metaphorical but physically obvious.

The Science Still Happening Here

NASA and multiple university research programmes continue active scientific work at Craters of the Moon because the monument’s value as a planetary analogue site has expanded rather than diminished since the Apollo era. Astrobiologists study the monument’s microbial communities — extremophile organisms living in the lava tube walls, cinder fields, and rift cracks — for clues about what biological signatures might look like in comparable volcanic environments on Mars or the icy moons of the outer solar system. The lava tube structures at Craters of the Moon are directly comparable to subsurface tube structures identified on Mars by orbital radar imaging, making the monument’s caves a legitimate research proxy for understanding how subsurface Mars habitats might function as refuges for microbial life. The Great Rift’s open crack system provides ongoing data for volcanologists studying how magma transport in rift zones operates at depth — the information has direct application to hazard assessment for the Yellowstone volcanic system 120 miles to the northeast, to which the Snake River Plain’s volcanic chain is geologically connected. This layer of active science running beneath the surface of the visitor experience gives Craters of the Moon a depth that most national monuments cannot match — every lava tube you crawl through is also a data point in an active research programme about the possibility of life on other planets.

Top 15 US Volcanic Sites: How Craters of the Moon Compares

Craters of the Moon sits within a network of exceptional volcanic destinations spread across the American West, each expressing a different chapter of the same underlying geological story. The table below gives you a sortable reference for planning a broader volcanic geology road trip — comparing each site by volcanic type, key feature, visitor crowd level, best season, and how closely it resembles the Craters of the Moon experience in terrain and character.

How to Build a US Volcanic Road Trip Around Craters of the Moon

Craters of the Moon’s position in south-central Idaho makes it the natural anchor of a Pacific Northwest volcanic circuit that covers more geological variety per mile than any other road trip routing in the American West. Driving northeast from Craters of the Moon, Yellowstone is 120 miles away — the hydrothermal counterpart to the lava field you have just walked, showing you what happens when a supervolcano expresses itself in geysers and hot springs rather than surface flows. Driving northwest from Craters of the Moon to Mount St. Helens in Washington adds the stratovolcano dimension — a 1980 eruption landscape where the blast zone is still recovering 45 years later in a succession of plant colonisation that volcanologists monitor as one of the most important ecological experiments in North American science. The Lava Beds National Monument in northern California is the closest geological twin to Craters of the Moon in the entire country — a basaltic shield landscape with over 700 lava tube caves, minimal visitor infrastructure, and the same combination of alien surface terrain and subsurface cave architecture that makes both monuments feel like the same geological conversation spoken in slightly different dialects. Connecting these four sites — Craters of the Moon, Yellowstone, Mount St. Helens, and Lava Beds — on a two-week Pacific Northwest road trip delivers every major volcanic type found in the continental United States: basaltic rift field, supervolcano caldera, stratovolcano blast zone, and basaltic shield lava landscape, each one a chapter in the same ongoing story about a continent still very much under construction.

What Makes Craters of the Moon Unique in This List

Among all 15 volcanic sites in the table above, Craters of the Moon occupies a position no other site exactly replicates — it is the only accessible rift zone in the continental United States where the geological process that created the landscape is still visibly and measurably active, the subsurface research still ongoing, and the surface terrain walkable without specialist equipment or guided mountaineering. Hawai’i Volcanoes offers active lava but requires a long-haul flight to reach. Yellowstone offers supervolcano scale but filters the volcanic experience through the visitor-friendly lens of geysers and boardwalks. Lava Beds comes closest in terrain character but lacks the NASA connection, the Great Rift access, and the rift zone’s planetary science dimension. What Craters of the Moon delivers that no comparable site provides in the same combination is the convergence of extreme geological accessibility — you can walk the rift crack, enter the lava tubes, summit the cinder cones, and navigate the backcountry wilderness all within a single national monument boundary at modest cost — with active scientific relevance to the question of whether life exists elsewhere in the solar system. That combination of deep geological time, ongoing planetary science, and landscape so convincingly extraterrestrial that NASA used it to prepare humans for another world puts Craters of the Moon in a category of American travel experience that is genuinely, verifiably singular.

What You Must Be Careful About

Heat is the primary and most underestimated hazard at Craters of the Moon. The black basalt surface absorbs sunlight and radiates it at ground level, creating conditions where the air temperature of 32°C translates to a ground-surface temperature exceeding 60°C — hot enough to cause burns through thin-soled footwear and to accelerate dehydration at a rate significantly faster than equivalent temperatures in shaded or vegetated environments. Carry a minimum of three litres of water per person for any full day of activity — there is no potable water anywhere on the trail system except at the visitor centre and campground taps. The lava surface itself is extremely sharp — a’a lava particularly will tear through standard hiking footwear, cut through exposed skin without any sensation of impact, and destroy bicycle tyres, tent floors, and any synthetic material dragged across it. Wear thick-soled trail shoes or boots with at minimum 5mm of sole protection for any off-trail walking, and never sit or rest directly on a’a lava without a seated pad beneath you. The lava tube caves require a working headlamp — not a phone torch — with fresh batteries because the interior of Indian Tunnel and Boy Scout Cave reaches areas of absolute darkness where a phone battery failure would leave you completely unable to navigate. The backcountry wilderness area has no water, no shade, no trail markers, and no cell service — backcountry permits are free but rangers brief all backcountry permit holders on minimum safety requirements before issuing, and solo backcountry travel is strongly discouraged. Flash thunderstorms develop over the Pioneer Mountains in summer afternoons with minimal warning and the flat lava field offers no shelter and no safe ground position during lightning — check the NOAA forecast at the visitor centre before any afternoon trail start and plan to be back at the vehicle or the visitor centre before 2:00 PM from July through August.

FAQ

How do I get to Craters of the Moon National Monument?

The monument entrance is on US Highway 20/26/93, 18 miles southwest of Arco, Idaho, and approximately 90 miles west of Idaho Falls. The nearest commercial airport is Idaho Falls Regional Airport served by Delta, United, and American Airlines from Salt Lake City, Denver, and other hub cities. From Idaho Falls, drive west on US-20 for 88 miles directly to the monument entrance. There is no public transportation to the monument — a rental car from Idaho Falls is the only practical access option.

Did NASA really train Apollo astronauts at Craters of the Moon?

Yes, and the training was scientifically substantive rather than symbolic. In August 1969, astronauts Eugene Cernan and Joe Engle spent a full day at the monument guided by geologists, learning volcanic rock identification, geological sampling technique, and terrain navigation — skills directly applicable to the geological fieldwork required on the lunar surface. Cernan later commanded the Apollo 17 mission, the last crewed Moon landing. NASA has described the field geology training at sites including Craters of the Moon as one of the most important preparations the Apollo programme undertook.

What are the lava tube caves like and do I need experience to enter them?

The accessible caves range from easy to moderately challenging. Indian Tunnel is the largest and most accessible — mostly walkable upright, well-lit near the entrance, and manageable for any physically capable visitor with a headlamp. Boy Scout Cave and Dewdrop Cave involve some crawling and squeezing through tighter passages and are better suited to confident, physically flexible visitors. Beauty Cave is intermediate. All cave visits require a free permit from the visitor centre, a working headlamp per person, and closed-toe shoes. No caving experience is required for the designated accessible caves, but claustrophobic visitors should preview the cave descriptions at the visitor centre before committing.

Is Craters of the Moon suitable for children?

Yes, with appropriate preparation. The North Crater Flow Trail, Spatter Cones, and Inferno Cone are all manageable for children with reasonable fitness. The cave system is an extraordinary educational experience for children with an interest in science or adventure. The key considerations are heat — children are more vulnerable to the radiant heat from the black lava surface than adults — and footwear, since the sharp lava surface will damage standard trainers and cause falls if children run on the uneven surface. Carry extra water specifically for children, apply sunscreen generously, and plan all strenuous activity before 10:00 AM in summer.

Can I camp inside the monument?

Yes. The Lava Flow Campground operates within the monument and offers 48 sites with tent pads, picnic tables, and access to drinking water and toilets — the only potable water source inside the monument. The campground does not have hookups and does not accept generator use after 10:00 PM. Sites are available first-come, first-served for most of the season, with reservations available through Recreation.gov for peak summer weekends. Camping inside the monument provides access to the dark sky resource, which is one of the finest in central Idaho — the Milky Way is visible with the naked eye on clear nights and the volcanic horizon adds a landscape dimension that no other campground in the region matches.

How much does it cost to visit Craters of the Moon?

The monument entrance fee is $25 per vehicle (valid for seven days), $20 per motorcycle, and $15 per individual entering on foot or bicycle. America the Beautiful annual national parks passes are accepted and provide free entry — the $80 annual pass pays for itself after four national park visits and is the most economical option for any traveler visiting multiple US national parks or monuments in the same year. Cave permits are free. Backcountry permits are free. Campground sites are $20 to $25 per night. There are no additional activity fees for any trail, lava field, or cave within the monument.

Is Craters of the Moon worth visiting if I have already been to Yellowstone?

Absolutely, and the two destinations are geologically complementary rather than repetitive. Yellowstone shows you the hydrothermal expression of a volcanic hotspot — geysers, fumaroles, and hot springs. Craters of the Moon shows you the direct lava expression of the same Snake River Plain volcanic system — the actual solidified rock flows, cinder cones, and rift cracks that Yellowstone’s geothermal activity is the surface symptom of. The two monuments are approximately 120 miles apart and make a natural pairing on any Idaho-Wyoming road trip. Craters of the Moon receives approximately 250,000 visitors per year versus Yellowstone’s four million, meaning the geological experience here is available at a scale and solitude level that Yellowstone’s popularity makes structurally impossible.

What is the best hiking trail for a first-time visitor?

The North Crater Flow Trail combined with the Inferno Cone summit is the best first-time pairing — together they take under three hours, require no specialist equipment, cover both the ground-level lava detail and the panoramic overview perspective, and represent the two most geologically informative experiences in the accessible monument. Start with the North Crater Flow Trail in the early morning for the interpretive signage context, then climb Inferno Cone while temperatures are still moderate, and use the summit panorama to plan the rest of your visit by identifying features visible in every direction across the lava field.