This mile - long lava tube cave was formed roughly 700 , 000 years ago by molten rock that erupted from a volcanic vent in nearby Hart Prairie . The top , sides and bottom of the flow cooled and solidified first , after which the insides of the lava river continued to flow emptying out the present cave . Ample evidence of how the tube was born is written in the rocks of which it is formed . Small wave - like undulations in the floor are the remains of ripples frozen in the last trickle of molten rock that flowed from the cave . Stone icicles hanging from the ceiling show where a final blast of volcanic heat caused the rock to partially re - liquefy and drip . Dress appropriately when you come to visit , with warm clothes and sturdy shoes . The cave is as cool as 42 ° even in summer , and you may even find some ice inside . The rocks are always sharp and slippery , too . Bring two or three sources of light , in case one happens to fail , it can be very dark one mile from the nearest light source . Portions of the cave which were defaced by graffiti , have been recently cleaned up . Today ' s more environmentally aware visitors take better care of such a unique resource and report vandals when they see them . Location : About 14 miles north of Flagstaff on paved highways and graveled Forest Roads . Travel time is about 45 minutes . Access : Drive 9 miles north of Flagstaff on US 180 and turn west ( left ) on FR 245 ( at milepost 230 ) . Continue 3 miles to FR 171 and turn south 1 mile to where FR 171 B turns left a short distance to Lava River Cave . Click on map at right for larger view . Season : You can visit Lava River Cave the year - round though you may need to ski to it in winter . Temperatures inside the cave remain roughly the same summer and winter . ( between 35 ° and 45 ° Fahrenheit ) . Attractions : Cool cave , Lava flow , Scenic drive , Wildlife viewing Facilities : Interpretive sign Notes : Wear warm clothes and sturdy shoes . Bring two or three light sourcesPlease don ' t deface cave surfaces , but do report anyone who does . Call 928 - 526 - 0600 . For more information contact : Peaks Ranger Station , 5075 N . Highway 89 , Flagstaff , Arizona 86004 , ( 928 ) 526 - 0866 Lava River Cave : A Natural MuseumNot all museums are in a building in a city . Lava River Cave is a natural museum where people can learn about history , geology , biology and cave climates . Unlike other museums , you can ' t just walk through a door to visit Lava River Cave . The entrance is actually a hole in the ground and the floor just inside is covered with large , slippery boulders . Also , conditions throughout the cave are always cold and dark . you will need to dress warmly , wear sturdy soled shoes and bring adequate lighting in order t make the most of your visit . A Little Bit of HistoryLumbermen working for the Saginaw and Manestee Lumber Company discovered Lava River Cave about 1915 . These lumbermen made less than $ 2 . 50 per day and each day was usually 12 hours of back - breaking work . Chainsaws were not popular yet and trees were felled using axes and 2 - man " buck " saws . Finding Lava River Cave was probably an exciting and welcome diversion for these hard working men of the early 1900 s . Homesteaders are said to have visited lava River Cave sometime around the turn of the century . According to historians , homesteaders would collect large quantities of ice from the cave . The ice was used for refrigeration , cooling drinks and maybe even to help create a rare summer treat - ice cream . A Frozen Moment in Geologic TimeLava River Cave probably formed within a few hours after a brief volcanic eruption . In comparison to other geologic events , like the cutting of a canyon or the movement of a glacier , Lava River Cave formed in the briefest of moments . Since the cave appears today much as it did shortly after its formation , it is indeed a " frozen moment " in geologic time . Lava River Cave is a unique kind of cave known as a " lava tube ". It is the longest cave of this kind in Arizona . Geologists believe lava River Cave was formed sometime between 650 , 000 and 700 , 000 years ago when molten lava erupted from a volcano near the present day site of Michelback Ranch . When the lava came to the surface its temperature was hotter than 2 , 000 degrees Fahrenheit ! Lava Flow FeaturesLava River Cave contains a variety of outstanding lava flow features . These features also used to exist outside the cave , but have long since been washed away by wind and rain , and overgrown by plants . The lava flow features in this cave include flow ripples , splashdowns , cooling cracks and lavasicles . Flow ripples can be observed on most of the floor throughout the last two thirds of the cave . This gives the floor the appearance of a frozen river . Actually the floor is a " frozen river " of lava which flowed through the cave shortly after the walls and ceiling hardened . Splashdowns appear to be rocks floating on the frozen river because they actually were . Shortly after the ceiling hardened a few rocks fell into the still flowing floor and floated downstream a little ways before the floor also hardened . Cooling cracks are long cracks in the floor , ceiling and walls . Some of these are six inches wide , three feet deep and over twenty feet long . These cracks formed as the lava cooled and hardened because lava shrinks when it cools . Lavasicles are very small icicle - like formations which formed after the walls and ceiling hardened . For some reason a hot blast of gas shot through the tube shortly after it formed and partially remelted the walls and ceiling . This caused drips of remelted lava to form and quickly hardened into lavasicles . The lava flow f 4 eatures within Lava River Cave may not seem particularly fragile , but they are over half a million years old and cannot be repaired or replaced . Please help keep the flow features unmarred for the enjoyment of future visitors . Nature ' s Ice BoxLava River Cave is an amazingly simple natural ice box . In fact , it could be considered the largest " refrigerator " in northern Arizona . on the hottest day of summer , when the temperature outside the cave is over 90 degrees , just inside the temperature is 35 degrees and sometimes there is ice ! There are two reasons that temperatures within the cave remain so cold : First , the lava rock which formed the cave is an excellent insulator . Its dark color and very dense composition prevent heat from traveling from the surface into the cave . Second , Lava River Cave is cold because of its general shape . The highest point of the cave is the entrance . Since hot air rises and cold air falls , cold air falls into the cave during winter and is trapped there throughout the summer . Creatures That Like The Cold and DarkLava River Cave is occasionally used by animals and insects . These include crickets , beetles , porcupines , squirrels and bats . All of these creatures are shy , and since so many people visit Lava River Cave , it is rate to actually see them while in the cave . We do know that animals use the cave because their droppings can be observed beneath rocks and along the walls . A Few Words About BatsBats are truly amazing little creatures which unfortunately have an undeserved bad reputation . A lot of people think bats are filthy , disease - ridden , flying mice . This is not the case . Bats are actually very clean and no more likely to contract rabies than your household pet . They are very important to the environment since they are the only major night - flying predator of insects . In one night some individual bats can nearly eat their own weight in insects ! Anyone who has had their share of mosquito bites ought to appreciate that . Bats and other creatures which like to live in cold , dark caves are very vulnerable to human disturbance . Please remember to treat any creatures you observe within Lava River Cave with respect and give them lots of room . Remember - you are a visitor in their home . Have A Safe VisitThe cold , dark conditions within Lava River Cave require some special precautions and preparation on the part of those planning a visit . The cave is not recommended for persons with physical handicaps because of extreme steep , narrow and rocky terrain . Each person in your group should carry three sources of light . Wear sturdy soled shoes that protect your from slipping or twisting your ankle . Wear warm Clothes . A hard hat will protect your from bumping your head . Leave notice with friends of your planned trip and return time . Enjoy your visit ! ConservationLitter and graffiti have been problems within Lava River Cave since the late 1960 s . For many years various groups and individuals have attempted to clean up the cave only to have their efforts thwarted by the return of more litter and new graffiti . A major restoration effort was organized in May of 1991 . Almost all the litter was packed out and much of the graffiti removed at that time . You can help maintain Lava River Cave for enjoyment of future visitors . Please don ' t build fires within the cave . Soot and ash can stain the floor and walls , and smoke disturbs animals which might use the cave . If you see litter within the cave , you can help by packing it out . Aside from being unsightly , litter can upset the ecosystem of the cave . If you see individuals writing on walls or committing other acts of vandalism within the cave , please report your observations to the Forest Service . Don ' t endanger yourself by confronting vandals , but if you can make a a description of the vandals or not the license plate number of their vehicle , you could help save the cave from further degradation .