Geologic Features and Processes Gallery
AbrasionHow rocks break down against other rocks.
AlluviumYoung fresh waterborne sediment found alongside streams.
AmygdulesMineral-filled bubbles in frozen lava.
AnticlineFolded rocks with the sides sloping away from each other.
AvulsionRiverbeds shift, ignoring our political boundaries.
Basalt ColumnsHexagonal jointing makes pencil-stacks in cooling lava.
BeddingThe most common feature of sedimentary rocks.
BioturbationA desert anthill illustrates organic weathering.
Black SandBlack sand is rare except in places like Hawaii.
BlocksBlocks are boulders being born from solid rock.
BoudinageFolding and stretching creates these sausage-y forms.
Braided StreamAlso called an anastomosing stream.
Cavernous WeatheringMechanical forces carve hollows into solid rock.
Channel CastThe fossil of a sand flow cutting into mud.
ColluviumWeathered material carried down from hills ready for rivers.
ConcretionsPseudofossils bound with mineral cement in curious shapes.
Contact MetamorphismLava has baked mud into brick-red rock.
Convolute LaminationSquirmy shapes in sedimentary rock beds.
DendriteNot fossils, but treelike mineral growths.
Desert PavementDeserts generally have a surface of stones like this.
Desert VarnishA close-up and explanation of this dark rock coating.
DikesExamples of sandstone and basalt intrusions.
Drag FoldRock layers bent along a fault.
ExfoliationThis erosional process sends slabs down a granite slope.
FiammeFlamelike signs of extreme volcanic conditions.
Flame StructureWisps of clay drawn up into a heavy overflow.
Flint NodulesPseudofossils of pure chert found in chalk.
Flute CastsTracks left in sedimentary rocks by fast waters.
FoldingSan Francisco's chocolate chert shows its wrinkles in an outcrop.
Foreset BedsSedimentary bedding laid down on a slope.
Frost HeaveMechanical action of ice is a mover of sediment.
Gas-Escape StructuresThey look similar to raindrop impressions.
GeodesRocky lumps with crystalline matter inside.
Geopetal StructureA sign of the ancient horizontal direction.
GeyserEveryone's favorite geologic personality.
Graded BeddingA reliable indicator of up and down.
GrusGranite weathers into this clean natural gravel.
Honeycomb WeatheringSmall, close-spaced hollows carved into solid rock.
HornitoSpurting lava builds little cones resembling old-fashioned ovens.
Hummocky Cross-BeddingStony evidence of sand-sweeping storms.
ImbricationA stacking pattern that points to ancient currents.
JointingOrganized cracks march in sets up a Sierra Nevada streambed.
Kink FoldsSharply creased shale beds in a Canadian roadcut.
KnockersA local name for the peculiar rocky knobs of mélange country.
LaminationA finely layered form of sedimentary structure shown in siltstone.
Landslide Picture GalleryExamples of several landslide types.
Lava PillowsSee Pillow Lava.
Liesegang BandingMysterious dark strips that overprint rocks.
Load CastsFootprints in mud of a seafloor avalanche.
Meromictic LakeRare lakes whose waters never overturn.
MudcracksA stony mosaic documents a dry period in a wet place.
Pele's HairWind stretches hot lava into blonde fibers.
PhenocrystsCrystals that stand out in igneous rocks.
Pillow LavaCommon on the seafloor, here exposed on land.
PseudofossilsA set of common items that fool fossil-hunters.
Retrograde MetamorphismHow a former garnet schist lost its garnets.
RipplesSigns of an ancient, gentle limestone sea.
Rip-Up ClastsSigns of an ancient seafloor avalanche.
Salt SprayA constant corrosive mist of salt goes from sea to land.
Scour-and-Fill StructuresTypical signs of turbidites.
Shatter ConesDistinctive shapes made in rocks by cosmic impacts.
SillAn igneous intrusion within the beds of another rock.
SlickensideThe "fault mirror" or polished surface of a former fault.
Spheroidal WeatheringThis near-surface process makes a basalt bulls-eye.
Stromatolitic StructureFossils of ancient bacterial mats.
SynclineA spectacular giant fold in the Canadian Arctic.
TafoniLarge hollows formed by cavernous weathering.
TalusCall this rock debris scree, too, if you like.
Thrust FaultIllustrated by the spectacular Keystone thrust of Nevada.
VeinA crack with a story.
VugA hole with a story.
XenolithsStones from strange places.