BEDROCK GEOLOGIC MAP AND VOLCANIC HISTORY

The bedrock geologic map (left; 1:50,000 scale) shows interpreted probable extents of map units that commonly are largely obscured by pyroclastic and other fragmental deposits on the 1:24,000-scale geologic map (sheet 1). Thick pyroclastic deposits in major 

valleys and low-lying areas are mapped as undivided deposits of the climactic eruption (unit cd). Large areas of talus, landslide, and sedimentary deposits within the caldera also are shown. Some bedrock units have been generalized for clarity.

A series of six maps (above) based on the bedrock geologic map depicts the interpreted volcanic history of the area during intervals selected to highlight pulses of volcanism: A, >350 ka; B, 350-260 ka; C, 260-180 ka; D, 180-80 ka; E, 80-40 ka; and F, 40-0 ka. 

Colored units in each figure indicate units emplaced during the interval represented by that figure, while gray units indicate those that are older. White area is regional rock in place before Mount Mazama volcanism. Unit areas are bounded by present exposures and 

have not been reconstructed to their original form. In many cases, only small patches represent units that clearly once were far more extensive. Because not every unit has been radiometrically dated, some age assignments may prove to be incorrect. See unit 

descriptions in Description of Map Units (pamphlet).

Aerial view east-northeast over Williams Crater cinder cone (basaltic andesite, unit bw; ca. 35 ka) and 

Hillman Peak (andesite, unit ah; 61±8 ka) on the west rim of Crater Lake caldera. Mingled basaltic andesite 

and dacite lava (unit mw; forested) issued from west (left) base of cinder cone, crater, and a tiny dome near 

Rim Drive. Treeless ground is mainly underlain by fine-grained, lithic- and crystal-rich ignimbrite (unit cu) 

and proximal lithic breccia (unit cb) of the climactic eruption. Buff-colored slope on top of rhyodacite flow 

of Llao Rock (unit rh; upper left) is the pumice-fall deposit of the climactic eruption (unit cp). Three 

rounded, forested hills beyond caldera rim in center distance are pre-Mazama rhyodacite domes: left to right, 

Bear Butte, Lookout Butte, and Scout Hill (unit rpb).

Northeast aerial view of Cleetwood Cove showing cliffs in rhyodacite lava of the Cleetwood flow at caldera 

rim on either side of tongue of remobilized lava (backflow) that oozed down the fresh caldera wall immediately following collapse of the caldera during the climactic eruption (Panorama G). Tree-covered mesa 

immediately beyond Rim Drive is the surface of the Cleetwood flow. Brick-red outcrops along Rim Drive are 

lava and climactic pumice-fall deposit where they oxidized atop the Cleetwood flow, which was still hot 

when the climactic eruption began. Moored light-blue tour boats and trail to boat landing and lake gauge 

visible at left and Palisade Point at right. Forested slope on left in middle distance is southeast flank of Timber 

Crater shield volcano.

View of Mount Scott looking southeast from Rim Drive, where the road traverses the southern of two thick 

flows of andesite of Grotto Cove (unit agc) near a picnic area. Mount Scott is a stratovolcano composed 

entirely of dacite (unit ds; ca. 420 ka) erupted from low lava fountains. Its hydrothermally altered interior is 

exposed in the cirque on right. Smooth dark cliff in foreground is vitrophyric north flank of the Redcloud 

Cliff rhyodacite flow (unit re; ca. 27 ka), where lava chilled against glacial ice and was subsequently sculpted 

by glacial action. Forested mesa in middle distance between Mount Scott and the Redcloud Cliff flow is Scott 

Bluffs, a coulee of dacite of Pumice Castle (unit dc; 71±5 ka, weighted mean).

Morning aerial view looking northwest up the valley of Sun Creek. Applegate Peak caps the prominent rock 

wall of the west side of Sun Notch at the caldera rim. Northwest caldera wall is visible on opposite side of 

Crater Lake through Sun Notch. Grayback Ridge in foreground is thick lava of pre-Mazama rhyodacite (unit 

rpb; ca. 410–460 ka). Forested valley wall on left consists of a thick unit rcs lava flow overlain by a unit rpb

lava flow. Upper slopes of Mount Mazama are underlain by andesite of Applegate Peak (unit aa; ca. 210–270 

ka), which onlaps unit rpb at Maklaks Pass between Grayback Ridge and Dutton Ridge in right center of 

middle distance. Flat floor of the broad glacial valley is underlain by at least 60 m of ignimbrite of the climactic eruption (unit cf), incised by Sun Creek.

Ignimbrite of the climactic eruption (unit cf) at Godfrey Glen (left center) on Munson Creek where it meets 

Annie Creek (below photograph), viewed from turnout on Highway 62. Deposit (~100 m thick) is compositionally zoned: juvenile blocks are uniform rhyodacite pumice in lower part, andesitic and gabbroic scoria in 

upper part, with a mixed zone in between. Color reflects emplacement temperature and compositional 

zonation of particulate matrix; stratigraphically higher and hotter material is dark gray. Thin, light-colored 

layer at top is the pyroclastic-flow deposit where it has been bleached by fumarolic alteration beneath a 1- to 

2-m-thick layer of fine ash. Pinnacle landforms in middle portion of ignimbrite are relatively erosion resistant 

tuff indurated by precipitation of silica and other minerals in pore spaces near gas-escape fractures and chimneys during cooling. High points on skyline are Garfield (left) and Applegate (right) Peaks on south caldera 

rim 6 km north-northeast of photographer.

View of Pumice Point looking northwest (Panoramas F and G). Lowest cliff is upper unit of andesite below 

Llao Rock (unit alu; 117±3 ka), which rests on glaciated surface of lower unit of andesite below Llao Rock 

(unit all, obscured by talus; 122±20 ka here). Middle cliff is dacite of Steel Bay (unit dsb; 116±5 ka). Highest 

cliff to right of pumice slope is andesite of Pumice Point (unit apu; 47±20 ka) that fills small paleovalley cut 

in fall deposit of dacite of Pumice Castle (unit dcp; 71±5 ka, weighted mean) resting on glaciated surface of 

unit dsb. The higher, broader part of the pumice slope consists of 6 m of pumice fall from the nearby Llao 

Rock vent (unit rhp) lying on glaciated units dcp and apu, overlain by 31 m of climactic pumice fall and 

interbedded nonwelded ignimbrite (unit cp), then truncated by 1 m of Wineglass Welded Tuff (unit cw; 

barely visible at top of pumice) that grades upward into 2 m of proximal-facies, lithic-rich climactic ignimbrite (unit cb).

View northeast of deposits of the climactic eruption above Skell Head, the most complete section on the 

caldera rim (right end of Panorama H). Climactic pumice fall (unit cp) forms pinkish-white slope and two 

prominent beds beside and above geologist. Horizontal boundaries between the four flow units of Wineglass 

Welded Tuff (Williams, 1942; unit cw) that make up the orange to brown cliff are marked by recesses and by 

relatively abundant, dark lithic fragments. The lower three flow units are partly welded and the highest flow 

is densely welded, grading up into black vitrophyre. Above the vitrophyre is a dark-colored slope of debris 

on proximal, lithic-rich climactic ignimbrite (unit cb).

View of southeast caldera wall (Panoramas J and K) from southwest shore of Crater Lake. Mount Scott is on 

the skyline at left, Kerr Notch in center, and Sun Notch at right. The notches are glacial valleys that were 

beheaded when the caldera collapsed during the climactic eruption ~7,700 yr ago. Dutton Cliff, between the 

notches, and the notch walls expose andesite of Applegate Peak (unit aa; ca. 210–270 ka). Andesite of Kerr 

Notch (unit ak; ~300–340 ka), dacite of Chaski Bay (unit db; ~350–380 ka), and andesite of phantom cone 

(unit apn; 403±12 ka) are exposed on either side of the talus below Dutton Cliff. Andesite of phantom cone 

is the oldest unit exposed in the caldera walls above lake level.

Aerial view towards north over east-facing scarp of Annie Spring fault. 

Basaltic andesite northwest of Pumice Flat (unit bf; 116±24 ka) forms 

north-south ridge in foreground that marks a fissure-vent system and also 

a small shield volcano (with arcuate buff-colored exposure at top) 

bounding forested Pumice Flat (right center). Forested hill due east of 

shield is Bear Bluff and coeval tuya (units rbb, 24±3 ka, and ab, respectively). Dark hill in middle distance is Arant Point (unit ati; 297±12 ka), 

the glaciated intrusive core of a cinder cone that is truncated on the east 

by the Annie Spring fault and that grew above the source vent for a tuya 

of the same unit (at) that forms a low mesa east of the fault. The Watchman, Hillman Peak, and Llao Rock are visible on the west and north 

walls of Crater Lake caldera; Mount Bailey is in the far distance. 

Between Arant Point and the caldera rim, in line with Llao Rock, is the 

source vent for dacite north of Castle Creek (unit dcn; 216±4 ka), cut and 

displaced down to the east by the Annie Spring fault.

View southwest of Applegate Peak and 280-m-high cliff below Sun 

Notch from phantom cone (Panorama K). Hydrothermally altered flowtop breccia weathers tan; whereas, dense lava flow interiors are dark, 

giving cliffs a horizontally striped appearance. Lava outcrop at lake level 

is andesite of phantom cone (unit apn; 403±12 ka nearby). Lava flows 

above phantom cone and below prominent buff-colored sedimentary 

layer near top of cliff are dacite of Chaski Bay (unit db; ~350–380 ka). 

Highest lava flows are andesite of Kerr Notch (unit ak; ~300–340 ka). 

Slope below rim at Sun Notch is proximal lithic-rich climactic ignimbrite (unit cb) overlying a few meters of climactic and Llao Rock 

pumice-fall deposits (units cp and rhp; not visible). Andesite of Applegate Peak (unit aa; ca. 210–270 ka) lava flows and breccia form their 

namesake and high cliffs at right. Two steep gullies in shadows below 

Applegate Peak follow traces of caldera-wall-parallel normal faults. 

Talus forming slope in lower foreground was shed from Dutton Cliff.

View north of spectacular columnar joints in andesite of Applegate Peak 

vitrophyre (unit aa; ca. 210–270 ka) below Wineglass (note geologist at 

lower right; Panorama H). Columns formed perpendicular to cooling 

surface as meltwater penetrated solidifying lava along growing fractures 

(joints) as a result of lava flowing against or beneath glacial ice. Cliff in 

distance is southeast margin of andesite of Roundtop (unit ar; 159±13 

ka), also an ice-bounded lava flow.

Aerial view northeast of Phantom Ship, a small island remnant of andesite of phantom cone (unit apn; 403±12 ka nearby). Resistant, hydrothermally altered lava flows that form Phantom Ship are the top of a buttress 

on the submerged caldera wall whose southwest side appears to be 

bounded by a northwest-trending dike (Bacon and others, 2002). Caldera 

wall in distance features Sentinel Rock and Kerr Notch (Panorama J). 

Mount Scott (right) and Cloudcap (left) are on skyline.

View from the south-southwest rim of Crater Lake caldera showing the caldera wall from Hillman Peak on 

the west to Cleetwood Cove on the north. Crater Lake fills half of the 8- by 10-km-diameter caldera formed 

during the climactic eruption of Mount Mazama volcano approximately 7,700 years ago. Volcanic rocks 

exposed in the caldera walls and on the flanks record over 400,000 years of eruptive history. The exposed 

cinder cone and andesite lava flows on Wizard Island represent only 2 percent of the total volume of postcaldera volcanic rocks that is largely covered by Crater Lake. Beyond Wizard Island, the great cliff of Llao Rock, 

rhyodacite lava emplaced 100-200 years before the caldera-forming eruption, dominates the northwest 

caldera wall where andesite lava flows at the lakeshore are approximately 150,000 years old.

Deposits of the climactic eruption exposed in road cut on Rim Drive above Cleetwood Cove. Well-bedded and sorted climactic 

pumice fall (unit cp) is light gray to white on left but becomes increasingly oxidized reddish and compacted (fused) stratigraphically 

downward where layers drape the underlying craggy top of the Cleetwood rhyodacite flow. The oxidation resulted from trapping of 

air and its reaction at high temperature with iron in the pumice through addition of heat from the lava, which also softened the pumice 

and caused it to compact. Because the climactic pumice-fall deposit is affected in this way only on the surface of the Cleetwood flow, 

these features are evidence that this lava was still hot at the time of the climactic eruption. The rhyodacite lava crops out below the 

bedded pumice at the lower left and at the lower right corner of the photograph. Boulders at top of left half of road cut and the large 

block to right of person are clasts in lithic breccia (unit cb) that here rests on the pumice fall without intervening Wineglass Welded 

Tuff. The lithic breccia and accompanying mafic scoria clasts were deposited by pyroclastic flows of the ring-vent phase of the 

climactic eruption, during collapse of Crater Lake caldera. The channel in unit cp in which the large lithic block occurs may have been 

cut by the same pyroclastic flows. Pumice lapilli and crystal-rich ash migrating downslope obscure part of the road cut exposure.

F

122°15' 122°07'30'' 122°

0 2 4 6 8 10 KILOMETERS

40-0 ka br

bw

cd

cd

dv

aw

bc

ab

cd

rbb

cd cd

cd

re

apc

r

amc

ae

t

t

sl

ls

sl

sl ls

t

rh

re

rh

cd

rs

bwn

mw

blcp

18±4

35±4

24±3

Sharp

Peak

Red

Cone

Castle

Point

 Little

Castle Creek

Bear

Bluff

Munson Valley

Redcloud

Cliff

Grouse

Hill

Llao

Rock

43°

42°52'30''

122°15' 122°07'30'' 122°

E 80-40 ka

arw

ad aww

aww

bh

ah

dwf

als

atw

bsc

dc

agc

asb

dc

agc dc

53±4

47±8

55±6

52±4

50±3

61±8

73±6

70±4

62±7

75±6

84±13

72±7

43±6

42±6

47±20

74±10

71±6

68±13

Scott Bluffs

Scoria

Cone

122°15' 122°07'30'' 122°

D 180-80 ka

bu

bf

acr

ar

atc

bui

bcnp

bcsp

amv

alb

dpe

dpt

am

dsb

all

alu abl

asc

111±9

164±11

116±24

136±8

172±15

118±48

98±8

155±6

87±15

102±10 159±13

122±20

117±3 116±5

150±9

131±18

172±11

116±9

109±19

137±17

153±12

137±10

Lookout

Butte

Scott

Creek

Union

Peak

Munson Valley

Crater

Peak

Timber

Crater

Pumice

Flat

C

43°

42°52'30''

122°15' 122°07'30'' 122°

260-180 ka

bo

bn

aa

dcn

aa

bmc

aa

aa

aa

dg

ag

ac

awe

220±67

244±4

211±16

224±9

269±12 

258±7

216±4

258±8

231±6

288±13

231±10

245±10

189±3

201±13

192±20 213±13

Oasis

Butte

Little Castle Creek

Maklaks

Crater

Desert

Cone

Bald

Crater

B

122°15' 122°07'30'' 122°

350-260 ka

dm

bx

baw

at

bx

ak

ak

dr

ao

bxn

bsw

dcc

arv

af

217±16

297±12

276±11

302±10

276±8

307±12

340±6

341±8 336±6

306±5

315±8

Arant

Point

Munson

Point

Whitehorse

Bluff

Rim

Village

Cavern Creek

Munson Ridge

A

43°

42°52'30''

122°15' 122°07'30'' 122°

>350 ka

bck

b

b

acc

b

bi

bac

bcw

rsc

rcs

rpb

rpb

dw

acs

dsc

dd

rsc

rpb

rcc

rsc

ds

rpb

db

su

rsc

apn dpn

bow

bwc

bcw

bbi

aaf

baf

bep

aq

bap btp

adsi bdp

bsr

as

asw

asw

db

blp

bcc

1879±22

587±18

517±15

651±28

623±16

670±12

403±12 346±20

354±4

351±12

382±8

1853±472 563±20

1058±16 1088±13

1275±14

415±11

724±5

422±10

416±7

355±8

448±8

605±25

468±9

612±8

1379±22

Anderson Bluffs

Mount

Scott

Lookout

Butte

Scott Creek

Bear

Butte

Dry

Butte

Maklaks

Pass

Scout

Hill

Pothole

Butte

Castle

Point

Rocktop

Butte

Whitehorse

Creek

Whitehorse

Bluff

Grayback Ridge

Sand

Creek

Quarry

Hill

6610'

3000 0 3000 6000 9000 12000 15000 18000 21000 FEET

SCALE 1:50 000

1 1/2 0 1 2 3 4 MILES

1 .5 0 1 2 3 4 5 KILOMETERS

b

dsbp

bsc

arv

122°15’ 122°07’30’’ 122°

122°15’ 122°07’30’’ 122°

43°

42°52’30’’

43°

42°52’30’’

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

SCIENTIFIC INVESTIGATIONS MAP 2832

SHEET 3 of 4

Pamphlet and CD-ROM accompany map

 

Geologic Map of Mount Mazama and Crater Lake Caldera, Oregon

By

Charles R. Bacon

2008

Any use of trade, product, or firm names in this publication is for 

descriptive purposes only and does not imply endorsement by the 

U.S. Government

For sale by U.S. Geological Survey, Information Services, Box 25286,

Federal Center, Denver, CO 80225, or call 1–888–ASK–USGS

Available on World Wide Web at http://pubs.usgs.gov/sim/2832/