What is Lava River Cave?
About 700,000 years ago a vent on Hart Prairie, on the west flank of the San Francisco Peaks, sent a river of basalt downhill. Its surface cooled and hardened into a crust while the lava inside kept flowing, and when the eruption stopped the molten core drained out and left the crust standing empty: a tube of rock, about a mile long, 20 to 30 feet across in its big rooms and a crouch in its tightest, with a floor of frozen ripples and the occasional collapsed slab. That is Lava River Cave, the longest lava tube in Arizona, at 7,684 feet in the ponderosa 14 miles north of Flagstaff.
There is no development beyond a vault toilet, a fee machine and a short path to the sinkhole where the ceiling fell in and made an entrance. You climb down through a jumble of boulders, and within a few steps it is black. The temperature holds between 35 and 45 degrees every day of the year; ice coats the entrance floor into early summer. You walk to the end, where the tube pinches shut, and you walk back. Nothing marks the route and nothing could, because there is only one way to go, but the floor is uneven enough that people turn ankles here every week in summer. Rangers do not patrol inside.
What you get is an hour or so of total darkness, cold air and strange rock, the best antidote to a Phoenix summer within three hours of Scottsdale. What you do not get is lighting, handrails, water, cell signal inside, help or a place to camp nearby. It is a hole in the forest, and you are responsible for yourself.
How to do Lava River Cave right
Pay like this. $5 per vehicle per day or $15 per week, paid at the automated machine at the trailhead; an America the Beautiful pass or Red Rock Pass is accepted. Day use only, no posted hours, no reservations.
Get there. Loop 101 north to I-17, I-17 north into Flagstaff, then Humphreys Street north out of downtown, which becomes US 180. About 9 miles out, at milepost 230, turn left on Forest Road 245 and follow it 3 miles of graded dirt to FR 171; turn left (south) for 1 mile, then left again onto FR 171B to the parking area. The dirt is fine for a sedan when dry and a trap when wet. About 2 hours 45 minutes from Old Town. The lot holds a few dozen cars and overflows onto the road shoulders on summer weekends.
Pick the season. The cave is open all year, and it is at its best in summer, when it is 50 degrees colder inside than the forest and the entrance ice lasts into June. FR 245 and 171 close for snow and mud, typically November into April or May, and the Forest Service’s winter alternative is a 4-mile walk or ski each way from US 180. Weekend afternoons are a conga line of headlamps; weekday mornings you will have it to yourself.
Bring three lights. Two or three light sources per person is the rule: a headlamp, a flashlight and a phone, plus spare batteries, because the walk to the far end and back takes an hour to an hour and a half of total darkness and a single dead light turns it into a crawl out by feel. Phones work as a backup light and nothing else; there is no signal inside.
Dress for a refrigerator. A warm layer, gloves, closed shoes with grip, and a helmet if you have one; the ceiling is lower than you think in the dark, and drops to a stoop in one stretch. The floor near the entrance is a boulder scramble and the middle section is rippled rock that catches toes.
Kids and dogs. School-age kids who can scramble and are not afraid of the dark do fine with a light each and a parent in front and behind. Not toddlers, and not anyone unsteady. Dogs are not allowed in the cave.
Camp elsewhere. Dispersed camping is prohibited within a mile of the entrance. The nearest developed camping is in Flagstaff; Fort Tuthill is 25 minutes, and Lockett Meadow is the pretty one on the other side of the Peaks.
Leave it as you found it. Do not mark the walls and do not leave trash; the cave has needed one big cleanup already. Turn all your lights off once, deep in, and stand still. Then turn them back on.
Skip it if you do not like dark, cold, rocky walking with no handrail and no help. Walk the aspens on Snowbowl Road instead, climb Humphreys Peak if you want effort, or go see the younger volcano at Sunset Crater. The day trips guide has the rest of the Flagstaff options.
The tube the loggers found
Lava River Cave is one small piece of the San Francisco volcanic field, the spread of cinder cones, lava flows and the stratovolcano of the Peaks that covers the country around Flagstaff. The tube formed when a vent on Hart Prairie erupted roughly 650,000 to 700,000 years ago and sent basalt flowing downhill. The walls still show both kinds of Hawaiian lava, ropy pahoehoe and rubbly aa, and the ripples on the floor are the last surface of the lava river as it drained away. At some point the roof collapsed near the upper end and made the sinkhole you climb into.
People have lived around these mountains for a very long time. The Peaks above the cave are sacred to the Hopi and the Navajo and to more than a dozen tribes in all, and Sinagua farmers lived across the volcanic field until Sunset Crater erupted in the 1080s and reshaped their world. No record we found ties the cave itself to any of them, and with an entrance hidden in a forest sinkhole it may simply have gone unnoticed, or unrecorded.
The written history starts with timber. Around 1915, lumbermen cutting ponderosa for the Saginaw and Manistee Lumber Company came across the entrance. For decades the tube was known as Government Cave, after Government Prairie and Government Peak beside it. Homesteaders in the area are said to have hauled blocks of ice out of the entrance through the summer to keep food cold, which is the most practical use anyone has made of it.
Recreation brought the predictable trouble. From the late 1960s the cave was a well-known Flagstaff outing, and litter and spray paint built up on the walls. A major cleanup in May 1991 removed most of the trash and much of the graffiti, and the Forest Service now manages it as a fee site, with a vault toilet, a machine that takes $5, and a sign telling you to bring lights. Dispersed camping within a mile of the entrance is banned, and the access roads still close every winter, so in practice the cave is a summer place, as it has been since the loggers found it.
Why it matters
Lava River Cave is the easiest way to stand inside the volcanic history of northern Arizona: the same field that built the Peaks, blanketed the Sinagua country in ash at Sunset Crater and laid the cinders that cover the Flagstaff forest. It is also a reminder that the Forest Service manages plenty of places with nothing but a sign and a toilet, and expects you to bring your own judgment. For a Scottsdale visitor the use is simple. On a 110-degree day in July, a three-hour drive gets you a cold, dark hour underground that nothing else in Arizona matches. Bring three lights per person, real shoes and a jacket, and go on a weekday morning.