Turn around, and at 0.3 miles, take the miles). Turn left, toward the French Round boiling — and plopping back down to stack right-hand road branch. Barn. Note the eastern end of Graben Dome. up around the spout. On one flow or another, The lava flows on the east side of the road Diamond Craters contains almost every known Park at the edge of the road on the are very complex — they are flank eruptions variation of these features. top of a rise where you can see the from Graben Dome. The geologists haven't 11 divide between Twin Craters at 9 0.7 miles even begun to figure out what exactly hap­ Northeast Dome (11 o'clock) differs from o'clock. Here you get a good view of pened here. the other structural domes, even though it is a Central Dome (10 to 1 o'clock). Remember variation on the same theme. By the time the that Ruptured Raven Ridge (11 o'clock along Almost 1 mile north of Big Bomb initial layer of Diamond Craters Basalt domed the skyline) is part of the original domal arch. 12 Crater, turn into the first road to the up, the layer was relatively cool and brittle. 4.8 miles left and park. The summit rock fractured into numerous, You are looking into the Central Crater nearly parallel, deep fissures — something Complex (10:30 to 11:30) which is a caldera. A On either side of the road are flank flows like corn bread inflating and cracking as it caldera is a depression similar to Crater Lake from Graben Dome. Look at the shallow bakes. Only a few of the but without water. As the supporting magma depression (8:30 to 10 o'clock), filled with fissures have been under the Central Dome blasted out in ex­ spatter features. Observe the spatter ridge measured. One of them is plosive eruptions, the stretched summit rock with the knob of spatter on top at 9 o'clock. 40 feet deep, eight feet collapsed into a caldera. The box-shaped Imagine a fire fountain powered by a very wide and nearly 250 feet depression with rounded ends is about one small amount of steam, showering spatter a long. As the supporting mile long, 3,500 feet wide and more than 200 few feet into the air. As the spatter falls back magma withdrew through feet deep. The Central Crater Complex has around the vent, it welds together into spatter flank eruptions on the more than 30 vents. In fact, the bumps you ramparts or walls (around fissures) and spat­ northern and eastern sides, a small graben see are rims of funnel-shaped craters inside ter rings and cones (around circular vents). formed on the southeastern slope. You can the caldera, similar to the craters at Red see the far wall (11 to 12 o'clock) running Bomb Crater. Near the end of the volcanic ac­ parallel to the skyline. tivity, pahoehoe lava flows formed a moat in­ Driblet spires, side the rim of the caldera. closely related Continue north on the country road and at to spatter 0.7 miles observe the spatter cones resulting Take a look at the dirt (tephra) under the features, from the flank eruptions. These features are sagebrush — it was blown out of the Center sometimes on private property, so please don't cross the Crater Complex. Most of the tephra in Dia­ form on fence. mond Craters came from Central Dome. Even pahoehoe At 1.9 miles, you come to the edge or toe of blocks of Devine Canyon Ash-flow Tuff sur­ flows as a the Diamond Craters flow. Devine Canyon faced from the bedrock beneath the Diamond gaseous spout Ash-flow Tuff can be seen on the hills to the Craters Basalts. The sharp rocks in the road develops, spit­ right. just before you arrive at South Dome are ting thick Pull off the road for a panoramic tephra from Central Dome. globs of mol­ view of the northern half of Diamond ten basalt a 13 Craters. Be safe and watch for traf­ Continue east to Big Bomb Crater (3.9 few feet into the air — like cream of wheat 3.8 miles fic as this stop is on a hilltop.

U.S. DEPARTMENT OF THE INTERIOR Bureau of Land Management Burns District Office HC74-12533 Highway 20 West Hines, Oregon 97738

Twin Craters — West Dome

Notes and References Although studies by geologists Dr. Bruce Nolf of Central Oregon Community College and Dr. Robert Bentley of Central Washington University have revised ideas on how Diamond Craters was formed, the 1964 paper by Norman V. Peterson and Edward A. Groh entitled "Dia­ mond Craters, Oregon" in 77?e Ore Bin, Vol.26, No. 2 pro­ vides a valuable description of the area. A recent, more technical work that ties Diamond Craters into the regional geology is "High Lava Plains, Brothers Fault Zone to Harney Basin, Oregon" printed in Guides To Some Volcanic Terranes in Washington, Idaho, Oregon and Northern California, Geoloqic Survev Circular 838. It was written by George Walker and Nolf. BLM would like to acknowledge the work of Dr. Pete Mehringer of Washington State University for data on the sediments in Malheur Maar. BLM-OR-GI-89-8-1122.32

A Self-Guided Tour Of: Diamond Craters Oregon's Geologic Gem

U.S. DEPARTMENT OF THE INTERIOR Bureau of Land Management Burns District «-. HC74-12533 Highway 20 West ' Hines, Oregon 97738

phonei503) 573-52*41;

Text by Ellen M. Benedict, Pacific University Keep your vehicle on on hard-packed road surfaces and obvious parking areas. Certain There's no other place in North America roads and trails are closed for rehabilitation. like Diamond Craters. Be careful or you might spend time stuck in That's the opinion held by scores of scien­ loose cinder, volcanic ash or clay. tists and educators who have visited and If you go hiking, carry drinking water. studied the area. It has the "best and most Watch out for rattlesnakes. If you come upon diverse basaltic volcanic features in the one, stay calm and allow the snake to glide United States and all within a comparatively away. small and accessible area," one geologist summarized. It took thousands of years of volcanic ac­ tivity to form Diamond Craters, but requires Yet visitors with little or no geologic train­ only a few seconds of carelessness or ing will probably see nothing more than acres thoughtlessness to destroy its features. Help of sagebrush and a few lava flows and BLM to protect and preserve Diamond craters. Craters. Please do not destroy or collect This guide will help you to locate and inter­ plants, animals or rocks. pret some of the outstanding features of Dia­ mond Craters that you might otherwise over­ Central Crater Complex look. You won't be an accomplished geologist How To Use This Guide after finishing the tour, but you will have a In the left margin are numbered paragraphs greater appreciation for the area labeled by Start Tour. Mileage begins halfway corresponding to the twelve stops along the between mile post 40 and 41 on one scientist as "a museum of basaltic 40-mile auto tour between State Highway 205 volcanism." 1 State Highway 205 at the junction at Diamond Junction to State Highway 78 at 0.0 miles to Diamond. Turn left. Princeton. The mileage below each number tells the distance from the last stop. Use your Diamond, Oregon, a small ranching com­ Travel and Hiking Hints odometer and the map to help locate stops. munity, was named in 1874 for Mace McCoy's Diamond Craters is located in the high Diamond brand. The nearby craters soon Features at stops correspond to points on became known as Diamond Craters. desert country about 55 miles southeast of a clock face. Imagine that you are standing in Burns, Oregon. It's an isolated place and the middle of a clock face. Twelve o'clock is You'll cross the Central Patrol Road of the some precautions should be taken when the road in front of you and 6 o'clock the road Malheur National Wildlife Refuge and the traveling in the area. behind. If you always align the clock face with Blitzen River at 1.0 miles. The Blitzen River First, Diamond Craters has no tourist the road, you should be able to locate the originates on Steens Mountain, the highest facilities. The nearest place where gasoline features. point in the southeastern skyline. is sold is at Frenchglen or Princeton. Park on the right edge of the soft globs of molten basalt) to violent blasts top of the other one. Be careful not to fall on road. of tephra (solid fragments ejected) thousands the sharp lava. Please, no vehicles are allowed. 2 of feet high. All kinds of activity took place at 2.6 miles On the left side of the road, north of Diamond Craters, creating an exceptional As you return to your vehicle, look closely the marshy area, is a panoramic view of Dia­ basaltic landscape. at the dirt under the sagebrush and notice the mond Craters. Start at the west. Follow the weathering tephra. Between here and the next edge (7 o'clock) of the lava flow east to West More than two-thirds of Diamond Craters is stop, Red Bomb Crater, you will be crossing Dome (8 o'clock). Central Dome (8:30) looks blanketed under basaltic tephra blasted from South Dome which is covered with tephra. like four or five humps along the skyline. vents within the six-mile wide "pancake." You can see tephra from here — it is the decom­ Red Bomb Crater. Pull into the Graben Dome (10:30) wears the crown of short parking loop road. Avoid get­ juniper trees. The two red cinder, dish-shaped posing volcanic ash forming the soil under the sagebrush on South Dome (10 o'clock) 7 ting stuck by staying on the firmly craters (9:30) midway below Graben Dome are 0.6 miles packed surface. More than one part of South Dome. and Graben Dome (12 o'clock). The tephra at Diamond Craters varies in size from volcanic vehicle has sunk to the hubs in this tephra. As you can tell from the map, Diamond ash to truck-sized blocks of rocks. While you stand on the crater rim and look Craters resembles a thin, rocky pancake with towards the southern skyline Steens Moun­ a few bumps. There is only a 550 foot range Directly ahead against the sky is Graben Dome (10:30 to 2 o'clock). This may appear to tain (7:30) rises nearly a mile above the from the lowest to highest point. Elevations Blitzen Valley. It is a west sloping fault block are from 4,150 to 4,700 feet above sea level. be an ordinary hill but it really is a remarkable feature of Diamond Craters. As the initial (6 to 9 o'clock) rising to an overall elevation of Have you noticed the rimrock on the buttes basaltic layer domed up, the rock stretched 9,773 feet above sea level. and the tablelands to the west, south and and fractured into long narrow blocks. The Jackass Mountain (11 o'clock), reaching east? The layer is the Devine Canyon Ash- supporting magma erupted out to the sides an elevation of 5,600 feet, is an east tilted flow Tuff Formation. This weathered, of the dome through weak fault block (9 to 11:30) of similar origin as reddish-brown layer may look solid, but spots, forming flank Steens Mountain. About 15 million years ago, it's actually composed of many thin layers flows. The summit approximately 75 layers of Steens Basalt of ash and rock all compacted blocks, without flooded out for miles from numerous vents. together—something like caramel support, col­ More recently, these layers fractured into corn. lapsed into elongated blocks which uplifted or down- a graben, a dropped, forming basins and ranges. Deep The rimrock came from shoebox- a volcanic vent under Diamond Craters there is probably located under Steens Basalt. present-day Burns, From here you get a good view of the Oregon. About 9.2 stream-cut Devine Canyon Ash-flow million years ago, a Tuff which forms the huge mass of hot uplands below the gases, volcanic ashes level of Steens bits of pumice and • Mountain. Closer other pyroclastics in, you can see (fire-broken rock) vio­ the southern part lently erupted. The blast of the Diamond —greater than the Craters lava flows, May 18,1980, eruption of mostly covered with Mt. St. Helens—deposited a tephra. layer of pyroclastics 30 to 130 feet thick over an area Red Bomb Crater, nearly almost 7,000 square 1,000 feet in diameter, formed miles! as hot basaltic magma rose through the water-saturated Pyroclastics are nor­ layers beneath South Dome. The mal behavior for source of the water was run-off magmas (subsurface — from Steens Mountain. The molten rocks) of water changed to steam, gen­ rhyolitic (a volcanic erating a confined steam ex­ material related to plosion (think of a hot water granite) composition. The tank exploding). Magma and broken silica (similar to Oregon rock shot upward and fained down beach sand) shaped around the vent, forming the cinder, or more content is so depres­ correctly, scoria, cone. Bombs and cinders high in the sion stuck together forming the dark layers rhyolitic ash with (11 o'clock). Volcanic actively resumed in a —75 percent open series of small explosive eruptions inside the for the Devine ends. big crater, forming the funnel-shaped craters. Canyon Ash- This dome Which vent erupted last? flow Tuff — has a main that the graben, 100 Now look at the bombs scattered along the magma is very feet deep, 7,000 parking loop road. You may see a breadcrust stiff and feet long and 1,250 feet bomb. Cooling basaltic globs became air­ pasty. Great wide, and two smaller ac­ borne. The surface chilled as the inside pressure cessory grabens crossing gases, mostly steam, expanded. That caused builds the main graben at right the outside of the globs to crack, forming a within the volcano and eventually it explodes. angles. You can see the breadcrust texture. Again, please leave the When pressure doesn't build up, rhyolitic open end of an accessory bombs in place. magma squeezes up like tooth paste, building graben (12:30) from here. a bulbous, steep-sided plug dome over the At Stop Number 11, you Return to your vehicle and continue west. vent. will view a flank flow from Graben Dome. Along the skyline you can see Ruptured Raven Ridge (1 o'clock), part of the original If you want to look at Devine Canyon Ash- The weakened summit rock of South Dome domal arch of Central Dome. flow Tuff more closely, stop at the roadcut (9 to 10:30) also collapsed, but irregularly as just before the junction (4.1 miles) where you high pressure steam explosions blasted the Between Red Bomb Crater and East Twin turn left to Diamond Craters. The supporting magma to the surface. From here, Crater on West Dome, btop Number 8, you unweathered rock is light gray. you can see three of the red cinder craters will come upon several dead end roads. Keep associated with South right on the main, well-traveled road until you Park on the rise at the right edge of Dome: Oval Crater (10:30, come to three roads branching off about 2.4 the road just past a junction com­ partially visible at the miles. Take the middle branch. You should 3 ing from the east. You should be skyline), Keyhole Explo­ be able to see two large craters in the side of 5.9 miles able to see the road to Diamond sion Crater (11 o'clock, West Dome. At about 2.6 miles, turn right on Craters disappearing in an S-shaped bend. base of domes) and Big the short spur road to the first crater. Bomb Crater (12 o'clock, Park in the circular area just below You are viewing the con­ foreground). Red Bomb the crater rim. This is East Twin tact between the Diamond Crater, at Stop Number 7, is a fourth red 8 Crater, an explosion crater of the Crater Basalts (dark lava cinder crater of South Dome. flow, 10 o'clock) and the 2.7 miles maar type, literally a hole in the As you travel to Big Bomb Crater Devine Canyon Ash-flow ground. A maar is a simple, circular depres­ (12 o'clock) you will cross a wall of Devine Tuff (reddish-brown, 12 sion surrounded by a low rim of ejected rock Canyon Ash-flow Tuff less than 0.1 miles o'clock). If a hole were fragments. Imagine the large blocks of rock from here. This wall is part of a kipuka, an drilled through shooting through the air from this crater! Is island of older rock completely surrounded by Diamond Craters Basalts, it would probably there evidence that magma came to the sur­ a younger lava flow. Continue on to the hit lake sediments and Devine Canyon Ash- face in this explosion? Look at the dark red junction by Big Bomb Crater. Turn left. flow Tuff. Can you visualize the down-tilted material at the eastern end of the rim — layer extending under the lava flow? Park immediately on the hard- where did it come from and what is it? The packed cinder by Big Bomb original walls were steeper and the crater How did Diamond Craters 5 Crater, a restored cinder pit. Here deeper. Gradually rocks broke loose, filling in form? Sometime in the 0.2 miles you can see cored bombs, which the crater and enlarging its diameter. last 25,000 years (geolo­ are marble-to-baseball-sized rocks. As the hot gists aren't sure just magma rises up through water-soaked layers, Continue west, taking the first when), molten basalt the water instantly changes to steam, caus­ branch to the right. At 0.2 miles, you spilled from deep cracks ing magma to explode and hurl rock frag­ 9 will see a short spur road going in the earth called 0.2 miles ments in the air. The fragments fall back into right to West Twin Crater. Looking fissures, then flooded the developing cinder cone and roll down into at the crater, did magma surface in this explo­ in a thin layer over a relatively dry lake bed. the vent. This is repeated several times as the sion? Note the large blocks of rock in the Before the initial layer cooled completely, fragments become coated with younger sagebrush. more basaltic magma injected underneath, molten rock. Do you see any bombs with creating six arching structural domes. Again as you travel toward Stop Number 10 glassy cores? The glassy cores were From here you can see two of the struc­ you'll find a maze of dead end roads branch­ analyzed and appeared to have remelted about ing off the main road. Stay on the main road tural domes: Graben Dome (10:30 to 17,000 years ago, suggesting that this cinder 12 o'clock) and South Dome (9:30 to 10:30). until you come to a wide curve on a rise with cone is that old. Please don't break open or a parking area on the north side of the road. Between here and the next stop, try to collect the bombs. separate Devine Canyon Ash-flow Tuff from The road ends about one-quarter of a mile far­ Diamond Craters Basalts. If you want to see the graben in Graben ther at the boundary between Diamond Dome, park here and hike up. Please, no Craters "Outstanding Natural Area" and the Park at the edge of the road where vehicles. Even four-wheel drives will damage Malheur National Wildlife Refuge. you can see lava flows to either the area. 4 side. You are looking at a scene of Park in the area on the rim of Dry 1.2 miles both quiet and explosive basaltic Continue westward. As you round Big Maar. This crater is a miniature eruptions. Bomb Crater, at about 0.2 miles, you will see 10 "Hole in the Ground" similar to the 0.5 miles the Lava Pit Crater Flow (10:30). Note that it gigantic one south of Bend, Lava flows, or streams of molten rock, at resembles the rather flat shield of a Viking Oregon. Dry Maar may not seem too exciting Diamond Craters contain an unusual diversity warrior. until you realize that it and water-filled of features. Notice the wrinkled surface on Malheur Maar (400 feet to the north) fit the the side of the pressure ridges (3 o'clock, Park in the small area by Lava Pit original definition of a maar which is "no close in). Imagine a very runny, gaseous Crater at the top of the rise. Walk magma surfacing during the explosion." molten basalt flowing out in a thin layer, the 6 over to the crater. You are on a crust chilling as the molten basalt remains 0.6 miles shield volcano. The word "volcano" Here you get a good view of the exposed red hot. The crust wrinkles — like the skin of refers both to the vent and to the hill, however surface of West Dome. Unlike the other a pudding — as the inside continues flowing. low, formed around the vent. domes that you've seen, the summit of West This is pahoehoe lava, noted for its smooth, Dome did not collapse or fracture. However, it wrinkled, ropy or billowy surface. Most first-time visitors to Lava Pit Crater is very interesting because six maar-type ex­ assume that this crater was formed by a huge plosion craters did form. Nolf Crater, on the The Lava Pit Crater (10 o'clock) is a shield explosion. Not so! Instead, pit craters form as north side of West Dome, is accessible only volcano. The pahoehoe flows at Diamond molten basalt wells up into a lava lake and by hiking over the very rough terrain. Multiple Craters were highly fluid — the only flows repeatedly overflow, gently building layer Explosion Crater is about 600 feet north of fluid enough to develop lava tubes, trenches, upon layer of tiny channels and mini-lava here where you see the broken wall on West collapse craters with and without natural tubes. The crater develops as the lava lake Dome. bridges, shield volcanoes, spatter cones and drains down under the flow leaving benches ramparts, kipukas, driblet spires and many at each lake level, which are easily seen here. Walk over to Malheur Maar and try to other features that you'll later see. The crater has enlarged as rocks have fallen estimate how deep the water is. The answer away from the rim, burying the original floor is six feet. Under the spring-fed lake, there are Lava flows are normal for the highly fluid under rock and dirt. about 50 feet of sediments which half fill the (or thin and runny) basaltic magmas. The maar. The sediments have been studied and it silica content is so low — it averages 49 per­ Stand on the high point of the western was found that the Crater has contained cent for the Diamond Craters Basalts — that crater rim where you can see the lava flow water for 7,000 years. Pollen, plant debris and the molten liquid floods all over the surface. with thick vegetation, just west of the Lava Pit layers of tephra accumulate rapidly in the Crater Flow. Now notice how barren the Lava The game changes, however, when molten lake, which is located at the boundary or Pit Crater Flow is. Which of the flows is basalt and water mix. This happens either as ecotone between the sagebrush and the older? It would be easy to assume the flow the magma rises through water-soaked layers desert shrub communities. All of this makes with the most plants is the oldest, but that is of earth or as the molten rock floods over the Malheur Maar one of the most significant incorrect. The Lava Pit Crater Flow is older — surface. The water changes to steam, power­ desert lakes between Mexico and Canada, it actually "lies under" the other flow. To prove ing the molten rock upwards with varying especially for studies of past climates. this, walk down and follow the contact be­ force — from quiet plops of spatter (small tween the two flows to see which one is on