Radiocarbon Dates from Volcanic Deposits of the 

Chaos Crags and Cinder Cone Eruptive Sequences 

and Other Deposits, Lassen Volcanic National Park 

and Vicinity, California 

By Michael A. Clynne, Robert L. Christiansen, Deborah A. Trimble, and John P. McGeehin 

Open-File Report 02-290

U.S. Department of the Interior 

U.S. Geological Survey 
ii

U.S. Department of the Interior 

GALE NORTON, Secretary 

U.S. Geological Survey 

Charles G. Groat, Director 

U.S. Geological Survey, Reston, Virginia 2008

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Suggested citation: 

Clynne, M.A., Christiansen, R.L., Trimble. D.A., and McGeehin, J.P., 2008, Radiocarbon 

dates from volcanic deposits of the Chaos Crags and Cinder Cone eruptive sequences 

and other deposits, Lassen Volcanic National Park and vicinity, California: U.S. 

Geological Survey Open-file Report 02-290, 18 p. [http://pubs.usgs.gov/of/2002/of02-290/].

Any use of trade, product, or firm names is for descriptive purposes only and does not 

imply endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the 

individual copyright owners to reproduce any copyrighted material contained within this 

report. 
iii

Contents 

Abstract ............................................................................................................................................ 1

Analytical Procedures...................................................................................................................... 1

Sample Descriptions ........................................................................................................................ 2

Cinder Cone .................................................................................................................................. 2

Chaos Crags.................................................................................................................................. 4

Other Deposits............................................................................................................................. 10

Discussion ...................................................................................................................................... 13

Cinder Cone ................................................................................................................................ 13

Chaos Crags................................................................................................................................ 14

References Cited............................................................................................................................ 17

Tables 

1. Uncalibrated radiocarbon ages of Cinder Cone deposits........................................................... 14

2. Uncalibrated radiocarbon ages of Chaos Crags deposits. ......................................................... 16

3. Stratigraphy of Chaos Crags after Muffler and others (1989) and Christiansen 

and others (2002) with average uncalibrated radiocarbon ages. ....................................... 17

Conversion Factors 

SI to Inch/Pound 

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Vertical coordinate information is referenced to the North American Vertical Datum of 1929 (NGVD 29). 

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27). 

Altitude, as used in this report, refers to distance above the vertical datum. 
1

Radiocarbon Dates from Volcanic Deposits of the 

Chaos Crags and Cinder Cone Eruptive Sequences 

and Other Deposits, Lassen Volcanic National Park 

and Vicinity, California 

By Michael A. Clynne, Robert L. Christiansen, Deborah A. Trimble, and John P. McGeehin 

Abstract 

This contribution reports radiocarbon ages obtained from charcoal, wood and other 

samples collected between 1979 and 2001 in Lassen Volcanic National Park and vicinity and a 

few samples from other nearby localities. Most of the samples are from the Chaos Crags and 

Cinder Cone eruptive sequences. Brief summaries are given of the Chaos Crags and Cinder 

Cone eruptive sequences. 

Analytical Procedures 

 Samples with the prefix USGS to the lab number were analyzed in the Menlo Park 

Radiocarbon Laboratory. Samples with the prefix WW were processed in the Reston 14C AMS 

preparatory laboratory and analyzed at the Center for Accelerator Mass Spectrometry (CAMS) at 

Lawrence Livermore National Laboratory. A field number is also given for each sample. The 

authors collected all samples unless otherwise noted in the sample description. 

Any sample preparation prior to submittal to the laboratory is noted in the sample 

description. Unless otherwise specified, all USGS prefix samples were pretreated with an acidalkali-acid (AAA) leaching process to remove contaminant carbon in the form of inorganic 

carbonates and organic soil acids. Samples were converted to CO2 by combustion, stored for at 

least 6 weeks to allow for decay of radon and counted in low-background, anti-coincidence gasproportional counters for at least 2,400 minutes. Additional details of the pretreatment and 

analytical process can be found in Robinson (1977) and Robinson and Trimble (1981). WW 

prefix samples were pretreated with an AAA pretreatment before conversion to CO2 and 

reduction with H2 to pure carbon in the form of graphite over an iron catalyst. Additional details 

of the sample handling and analytical process can be found in McGeehin and others (2001) and 

Roberts and others (1997) respectively. 

Ages published herein are reported as received from the analytical laboratories. No 

calibration to the absolute radiocarbon time scale has been performed. All ages are calculated 

using the Libby 5,568-year half-life for 14C and with δ13C=-27 unless otherwise noted, and are 

given in years BP (before present, defined as 1950). Errors as stated include one standard 

deviation of counting statistics and an additional uncertainty attributable to isotope fractionation, 

counter variables and sample processing. Ages for these samples published in other venues may 

vary slightly as a function of calibration to the absolute time scale or by calculation of weighted 

averages for multiple analyses. 
2

Sample Descriptions 

Cinder Cone 

Laboratory number Field number age (yrs B.P.) 

USGS 2493 LC86-927 250 ± 35 

Wood collected from standing snag in the Cinder Cone ash field, approximately 1.4 km 

south of Cinder Cone (Prospect Peak 7-1/2′ quadrangle, 40 ̊ 32.12′ 121 ̊ 19.48′). Sample 

consists of wood from the outermost preserved 10 rings of tree eroded by windblown ash. The 

snag is approximately 2m from edge of the Painted Dunes lava flow, rooted in till underlying the 

Cinder Cone ash deposit, and was probably killed by the eruption. Sample cleaned of a small 

amount of lichen, and weathered surface removed by hand. Sample approximately dates the 

Cinder Cone eruption. 

USGS 2613 LC87-1146 440 ± 46 

Wood collected from standing snag partially buried by lava along the eastern margin of 

the Fantastic Lava Beds flow, approximately 2.0 km east of Cinder Cone (Prospect Peak 7-1/2′

quadrangle, 40 ̊ 32.65′ 121 ̊ 17.77′). Sample consists of wood from the outermost preserved 10 

rings of tree without bark. The snag is leaning and is rooted in till underlying the Cinder Cone 

ash deposit and surrounded by blocks from the lava. An unknown amount of wood has been lost 

from the tree trunk by erosion. Sample cleaned of a small amount of lichen, and weathered 

surface removed by hand. Sample provides a maximum age for the Cinder Cone eruption, as the 

tree appears to have been significantly eroded or may have been already dead at the time of the 

eruption. 

USGS 2615 LC88-1273A 265 ± 63 

Sample collected from forest duff beneath the Cinder Cone ash deposit approximately 2.3 

km southwest of Cinder Cone (Prospect Peak 7-1/2′ quadrangle, 40 ̊ 32.17′ 121 ̊ 20.52′). 

Sample overlies soil developed on Chaos Crags ash, and underlies the Cinder Cone ash deposit. 

Sample consists of charred platelets of Jeffrey Pine bark. Modern rootlets picked and sample 

cleaned of extraneous soil material by hand. Sample provides a direct date for the Cinder Cone 

eruption. 

USGS 2663 LC87-1158 430 ± 50 

 Sample collected from stump partially buried by lava along the eastern margin of the 

Fantastic Lava Beds flow, approximately 2.0 km east of Cinder Cone (Prospect Peak 7-1/2′

quadrangle, 40 ̊ 32.63′ 121 ̊ 17.80′). Sample consists of charcoal collected from the outermost 

preserved 10 rings of the partially burned stump which lacks bark. The stump is rooted in till 

underlying the Cinder Cone ash deposit and surrounded by blocks from the lava. The tree was 

cut down sometime after the eruption, perhaps for tree-ring studies (Diller, 1891; Finch, 1937). 

An unknown amount of wood has been lost from the tree trunk by erosion. Sample provides a 

maximum age, as the stump appears to have been significantly eroded or may have been already 

dead at the time of the eruption. 
3

USGS 2664 LC87-1218 405 ± 42 

Sample collected from snag lying on the lava along the western margin of the Painted 

Dunes lava flow approximately 1.2 km southwest of Cinder Cone (Prospect Peak 7-1/2′

quadrangle, 40 ̊ 32.26′ 121 ̊ 19.57′). Sample consists of charcoal collected from the outermost 

preserved 10 rings of tree without bark. The snag is charred on the side facing the lava flow. 

The stump of this tree is buried beneath either the ash or the lava. An unknown amount of 

wood has been lost from the tree trunk by burning and erosion. Sample provides a maximum age, 

as the tree appears to have been significantly eroded or may have been already dead at the time 

of the eruption. 

USGS 2665 LC87-1174 200 ± 50 

Sample collected from standing snag partially buried by Cinder Cone lava flow, 

approximately 0.1 km north of intersection of the lava flow with the northeast corner of the 

shoreline of Snag Lake (Prospect Peak 7-1/2′ quadrangle, 40 ̊ 31.44′ 121 ̊ 18.28′). Sample 

consists of wood collected from the outermost preserved 10 rings of tree without bark. The snag 

is rooted in till underlying the Cinder Cone ash deposit and is surrounded by blocks of lava from 

the flow front. Sample cleaned of a small amount of lichen, and weathered surface removed by 

hand. Sample provides a minimum age, as the tree may not have been killed in the eruption, but 

nevertheless approaches the age of the Cinder Cone eruption. 

USGS 2769 LC89-1480 140 ± 42 

Sample collected from stump of tree in the Cinder Cone ash field, approximately 2.1 km 

southwest of Cinder Cone (Prospect Peak 7-1/2′ quadrangle, 40 ̊ 31.9′ 121 ̊ 20.2′). Sample 

consists of wood collected from the outermost preserved 10 rings of tree without bark. The snag 

is rooted in soil beneath Cinder Cone ash on the underlying andesite of Fairfield Peak. Sample 

cleaned of weathered surface by hand. Sample provides a minimum age, as the tree was 

probably not killed by the Cinder Cone eruption and continued to grow for at least several 

decades. 

USGS 3080 LC91-1615 200 ± 50 

Sample collected from submerged log near northwest shore of Snag Lake (Prospect Peak 

7-1/2′ quadrangle, 40 ̊ 31.3′ 121 ̊ 18.7′). Eruption of the Painted Dunes lava flow from Cinder 

Cone created Snag Lake by damming the Grassy Creek drainage from the Central Plateau of 

Lassen Volcanic National Park. In the late 1980s, the level of Snag Lake was lowered by 

drought, and many logs were exposed on the lake bed. Sample consists of wood from the 

outermost available portion of a log and was collected by Chris Williams, National Park Service 

(different log than sample USGS 3641). The log was partially decomposed and did not have any 

intact bark. This sample had thin, closely spaced rings and was probably a small tree. Algae 

were removed by scraping the outer surface of the sample. The analytical result and relationship 

of this sample to the lake suggest that it might directly date the eruption of Cinder Cone. 

However, the date could be either a minimum or maximum age depending on how quickly the 

tree was drowned by the rising lake, whether it was already dead, or whether it was killed by 

some unrelated event and fell into the lake. See USGS 3641 from the same locality. 
4

USGS 3641 LC91-1617 270 ± 42 

Sample collected from submerged log near northwest shore of Snag Lake (Prospect Peak 

7-1/2′ quadrangle, 40 ̊ 31.3′ 121 ̊ 18.7′). Eruption of the Painted Dunes lava flow from Cinder 

Cone created Snag Lake by damming the Grassy Creek drainage from the Central Plateau of 

Lassen Volcanic National Park. In the late 1980s, the level of Snag Lake was lowered by 

drought, and many logs were exposed on the lake bed. Sample consists of wood from the 

outermost available portion of a log and was collected by Chris Williams, National Park Service 

(different log than sample USGS 3080). The log was partially decomposed and did not have any 

intact bark. Algae were removed by scraping the outer surface of the sample. The analytical 

result and relationship of this sample to the lake suggest that it might directly date the eruption of 

Cinder Cone. However, the date could be either a minimum or maximum age depending on how 

quickly the tree was drowned by the rising lake, whether it was already dead, or whether it was 

killed by some unrelated event and fell into the lake. See USGS 3080 from the same locality. 

USGS 3683 LC95-2139A 270 ± 42 

Sample collected from forest duff beneath the Cinder Cone ash approximately 1.4 km 

north of Butte Lake Ranger Station (Prospect Peak 7-1/2′ quadrangle, 40 ̊ 34.75′ 121 ̊ 18.26′). 

Sample overlies soil developed on Chaos Crags ash and underlies Cinder Cone ash deposit (10 

cm of unit 2 and 30 cm of unit 3 of Heiken (1978); unit 1 missing at this locality. Sample 

consists of charred platelets of Jeffrey Pine bark. Modern rootlets picked out by hand and 

sample cleaned of extraneous soil material by washing in water. Sample directly dates the 

Cinder Cone eruption. 

USGS 3684 LC95-2144 255 ± 46 

Sample collected from tree almost completely buried by lava along the northwest margin 

of the Fantastic Lava Beds lava flow from Cinder Cone (Prospect Peak 7-1/2′ quadrangle, 40 ̊ 

33.24′ 121 ̊ 18.59′). Sample consists of the outer 10 rings of an aspen tree that was growing 

along the margin of ancient Lake Bidwell (Diller, 1891). Lake Bidwell was considerably 

reduced in size by the Cinder Cone lava flows, and its remnant is now Butte Lake (Clynne and 

others, 2000). Although the tree trunk lacked bark, the sample was collected from the outer part 

of the tree where two branches come together and indicate that the sample was from the living 

surface of the tree (see illustration in Clynne and others, 2000). Sample was covered with moss, 

which was removed by hand. This sample is considered to be the best of the Cinder Cone 

samples, most accurately dating the eruption of the Cinder Cone lava flows. 

Chaos Crags 

Map units designated for samples from the volcanic deposits of the Chaos Crags eruptive 

sequence are those of Christiansen and others (2002). Unit pc as mapped by them consists of an 

initial fallout pumice and three pyroclastic flows here referred to by their stratigraphic 

relationships as the lower, middle and upper pyroclastic flow. A widespread fallout pumice 

deposit is also associated with the upper pyroclastic flow. 
5

Laboratory number Field number age (yrs B.P.) 

USGS 1351 LC81-737 1100 ± 67 

 Charcoal collected from the fall deposit related to the upper pyroclastic flow from Chaos 

Crags in the Devastated Area (West Prospect Peak 7-1/2′ quadrangle, 40 ̊ 30.75′ 121 ̊ 29.68′). 

The fall deposit is overlain by May 1915 deposits at this locality. Sample may have been slightly 

reworked by the 1915 eruption. Sample consists of a small lump of charcoal. Modern rootlets 

were picked out by hand. Sample dates the last major explosive phase of the Chaos Crags 

eruptive sequence (unit pc, Christiansen and others, 2002). 

USGS 1353 LC81-848 275 ± 63 

Wood collected from one of a group of emergent and submerged trees standing in 

approximately 8m of water near the Manzanita Creek inlet to Manzanita Lake (Manzanita Lake 

7-1/2′ quadrangle, 40 ̊ 32.08′ 121 ̊ 33.93′). Sample consists of a single piece of wood from 

outer portion of a submerged but still standing tree trunk. Bark was not intact on the tree, and 

the trunk was overgrown by live algae. Sample collected by Gary Fry, National Park Service. 

Dead and live algae scraped off by hand. Sample dates death of tree by drowning when Chaos 

Jumbles rockfall avalanche (unit scj, Christiansen and others, 2002) dammed Manzanita Creek 

and formed Manzanita Lake. See USGS 1847 and 1848. 

USGS 1606 LC82-203 1105 ± 58 

 Charcoal collected from fall deposit related to the upper Chaos Crags pyroclastic flow in 

the Devastated Area (West Prospect Peak 7-1/2′ quadrangle, 40 ̊ 30.70′ 121 ̊ 28.73′). The 

deposit is overlain by May 22, 1915 pyroclastic flow at this locality. Sample may have been 

slightly reworked by the 1915 eruption. Sample consists of a small lump of charcoal. Modern 

rootlets picked out by hand. Sample dates the last major explosive phase of the Chaos Crags 

eruptive sequence (unit pc, Christiansen and others, 2002). 

USGS 1607 82LP-16C 1480 ± 58 

 Charcoal from an ash deposit underlying colluvially reworked Chaos Crags ash and 

pumice, approximately 2 km southeast of the northern end of Manzanita Lake (Manzanita Lake 

7-1/2′ quadrangle, 40 ̊ 31.44′ 121 ̊ 33.36′). Sample consists of bits of charcoal disseminated 

throughout a 60-cm thick deposit of fine yellowish ash. The deposit has a weakly developed soil 

and overlies till of Raker Peak (Christiansen and others, 2002). The deposit is widespread in the 

area around Chaos Crags and Manzanita Lake, but has been reworked by colluvial processes and 

originated from a volcanic eruption much older than the age of the dated sample. The location of 

the vent for this deposit is unknown, but likely is related to the emplacement of Lassen Peak at 

27 ka. Modern rootlets picked out by hand and sample washed in water to remove adhering 

material. Sample provides a lower limit for the age of the Chaos Crags eruptive sequence. 

USGS 1608A 82LP26-765A 1250 ± 67 

 Charcoal from section of Chaos Crags pyroclastic flows exposed in north wall of borrow 

pit at end of National Park Service road in Anklin Meadows (West Prospect Peak 7-1/2′

quadrangle, 40 ̊ 31.67′ 121 ̊ 29.09′). Sample collected from 10 cm below top of uppermost 

Chaos Crags pyroclastic flow at this locality, directly overlain by May 19, 1915 debris flow. This 

pyroclastic flow contains abundant, large, conspicuously breadcrusted pumice blocks (unit pc, 

Christiansen and others, 2002). Sample consists of a single 10-cm piece of charcoal with 10 
6

thick tree rings. Modern rootlets picked out by hand. Because the position of this sample within 

its host tree is unconstrained, the date obtained is a maximum age for this deposit; date is 125 to 

205 years older than that of a stratigraphically older sample from the same section (USGS 

1609A, B). Sample puts a maximum on cessation of pyroclastic activity in the Chaos Crags 

eruptive sequence. See USGS 1609A, 1609B and 2343 from the same locality. 

USGS 1609A 82LP27A 1125 ± 54 

 Charcoal from section of Chaos Crags pyroclastic flows exposed in north bank of borrow 

pit at end of NPS service road in Anklin Meadows (West Prospect Peak-7 1/2′ quadrangle, 40 ̊ 

31.67′ 121 ̊ 29.09′). Sample collected from outer 10 rings just below intact bark of a 70-cmdiameter Jeffrey Pine tree trunk in the oldest of the three Chaos Crags pyroclastic flows at this 

locality (unit pc, Christiansen and others, 2002). Distilled sap from the sampled tree trunk 

penetrates into the overlying pyroclastic flow and indicates that the two flows cooled as a single 

unit. Modern rootlets picked out by hand. Sample dates initiation of Chaos Crags eruptive 

sequence and duplicates USGS 1609B. See USGS 1608A, 1609B and 2343 from the same 

locality. 

USGS 1609B 82LP27B 1035 ± 54 

 Charcoal from section of Chaos Crags pyroclastic flows exposed in north bank of borrow 

pit at end of NPS service road in Anklin Meadows (West Prospect Peak 7-1/2′ quadrangle, 40 ̊ 

31.67′ 121 ̊ 29.09′). Sample collected from outer 10 rings just below intact bark of a 70-cmdiameter Jeffrey Pine tree trunk in the oldest of the three Chaos Crags pyroclastic flows at this 

locality (unit pc, Christiansen and others, 2002). Distilled sap from the sampled tree trunk 

penetrates into the overlying pyroclastic flow and indicates that the two flows cooled as a single 

unit. Modern rootlets picked out by hand. Sample dates initiation of Chaos Crags eruptive 

sequence and duplicates USGS 1609A. See USGS 1608A, 1609A, and 2343 from the same 

locality. 

USGS 1612 82LP29-330 1065 ± 58 

 Charcoal from section of Chaos Crags pyroclastic flows exposed in the south bank of 

Manzanita Creek (Manzanita Lake 7-1/2′ quadrangle, 40 ̊ 31.82′ 121 ̊ 33.08′) near measured 

section 1 of Crandell and others (1974). Sample consists of disseminated bits of charcoal 

collected from basal 5 cm of the lowermost Chaos Crags pyroclastic flow at this locality (unit pc, 

Christiansen and others, 2002). This pyroclastic flow directly overlies till. Modern rootlets 

picked out by hand and sample washed in water to remove adhering material. Sample dates 

initiation of the Chaos Crags eruptive sequence. See samples USGS 1610 and 1611 from the 

same locality. 

USGS 1614 82LP30A 1175 ± 54 

 Charcoal from section of Chaos Crags pyroclastic flows exposed in the south bank of 

Manzanita Creek approximately 75m southeast of NPS water tank (Manzanita Lake 7-1/2′

quadrangle, 40 ̊ 31.90′ 121 ̊ 33.15′). This locality is the same as measured section 1 of Crandell 

and others (1974). Sample collected from basal 10 cm of the lowest Chaos Crags pyroclastic 

flow at this locality (unit pc, Christiansen and others, 2002), which directly overlies till. Sample 

consists of twigs up to 1-cm diameter, probably manzanita wood. Modern rootlets picked out by 
7

hand and sample washed in water to remove adhering material. Sample dates initiation of Chaos 

Crags eruptive sequence. See USGS 1616, 2346 and 2347 from the same locality. 

USGS 1616 82LP30D 1090 ± 54 

 Charcoal from section of Chaos Crags pyroclastic flows exposed in the south bank of 

Manzanita Creek approximately 75m southeast of NPS water tank (Manzanita Lake 7-1/2′

quadrangle, 40 ̊ 31.98′ 121 ̊ 33.15′). This locality is the same as measured section 1 of Crandell 

and others (1974). Sample collected from basal portion of the uppermost Chaos Crags 

pyroclastic flow at this locality and contains abundant, large, conspicuously-breadcrusted pumice 

blocks (unit pc, Christiansen and others, 2002). Sample consists of small twigs from an 8-cmdiameter log with intact bark. Modern rootlets picked out by hand and sample washed in water 

to remove adhering material. Sample dates the last major explosive phase of the Chaos Crags 

eruptive sequence. See USGS 1614, 2346 and 2347 from the same locality. 

USGS 1847 LC83-396A 265 ± 42 

Wood collected from one of a group of emergent and submerged trees standing in 

approximately 8m of water near the Manzanita Creek inlet to Manzanita Lake (Manzanita Lake 

7-1/2′ quadrangle, 40 ̊ 32.08′ 121 ̊ 33.93′). Sample consists of the outermost 10 growth rings of 

the closer-to-shore of two standing Jeffrey Pine trees emergent from the lake. Bark not intact on 

the tree, but smooth outer surface indicates that there was probably no erosion of the tree. Small 

amount of algae growing on the surface was scraped off the sample by hand. Sample dates death 

of tree by drowning when Chaos Jumbles rockfall avalanche (unit scj, Christiansen and others, 

2002) dammed Manzanita Creek and formed Manzanita Lake. See USGS-1353 and 1848. 

USGS 1848 LC83-396B 305 ± 58 

Wood collected from one of a group of emergent and submerged trees standing in 

approximately 8m of water near the Manzanita Creek inlet to Manzanita Lake (Manzanita Lake 

7-1/2′ quadrangle, 40 ̊ 32.08′ 121 ̊ 33.93′). Sample consists of the outermost 10 growth rings of 

the farther-from-shore of two standing Jeffrey Pine trees emergent from the lake. Bark not intact 

on the tree, but smooth outer surface indicates that there was probably no erosion of the tree. 

Small amount of algae growing on the surface was scraped off by hand. Sample dates death of 

tree by drowning when Chaos Jumbles rockfall avalanche (unit scj, Christiansen and others, 

2002) dammed Manzanita Creek and formed Manzanita Lake. See USGS-1353 and 1847. 

USGS 2047 LC84-440 1005 ± 58 

 Charcoal from composite section of Chaos Crags pyroclastic deposits collected from 

hand-dug pit along Manzanita Creek west of the NPS fire road (Manzanita Lake 7-1/2′

quadrangle, 40 ̊ 30.21′ 121 ̊ 32.20′). Sample consists of small bits of charcoal from about 50 

cm below the top of an 80-cm-thick ash layer directly overlying till. Sample underlies a pink 

layer correlated to the boundary between the middle and upper of the three Chaos Crags 

pyroclastic flows (unit pc, Christiansen and others, 2002), which is overlain in turn by ejecta 

correlated with the fall deposit associated with the upper pyroclastic flow. Modern rootlets 

picked out by hand and sample washed with water to remove adhering material. Sample dates 

initiation of the explosive phase of the Chaos Crags eruptive sequence. 
8

USGS 2049 LC84-645A 1065 ± 58 

 Charcoal collected from a 3-m-thick section of Chaos Crags pyroclastic flows in streambank exposure on Manzanita Creek (Manzanita Lake 7-1/2′ quadrangle, 40 ̊ 30.57′ 121 ̊ 31.81′). 

Sample consists of outer 5 rings collected from beneath intact bark on charcoalized log in lower 

of the two pyroclastic flows at this locality (the lower and middle pyroclastic flows from Chaos 

Crags; unit pc, Christiansen and others, 2002). Pyroclastic flows underlain by till and overlain 

by May 22, 1915 debris flow from Lassen Peak. Modern rootlets picked out by hand. Sample 

dates initiation of Chaos Crags eruptive sequence. 

USGS 2343 LC85-711 1045 ± 42 

 Charcoal from section of Chaos Crags pyroclastic flows exposed in north wall of borrow 

pit at end of NPS service road in Anklin Meadows (West Prospect Peak 7-1/2′ quadrangle, 40 ̊ 

31.67′ 121 ̊ 29.09′). The sample is from the youngest pyroclastic flow at this locality, contains 

abundant, large, conspicuously breadcrusted pumice blocks and is the upper of the three Chaos 

Crags pyroclastic flows (unit pc, Christiansen and others, 2002). Overlies older Chaos Crags 

pyroclastic flows and is overlain by May 19, 1915 debris flow. Sample collected from outer 10 

rings just below intact bark of a charcoalized log. Modern rootlets picked out by hand. Sample 

dates the last major explosive phase of the Chaos Crags eruptive sequence. See USGS 1608A, 

1609A, and 1609B from the same locality. 

USGS 2344 85LP170 1015 ± 42 

 Charcoal from the fall deposit associated with the upper pyroclastic flow from Chaos 

Crags, approximately 0.5 km southeast of Old Boundary Spring (West Prospect Peak 7-1/2′

quadrangle, 40 ̊ 31.2′ 121 ̊ 28.5′). Sample collected at base of colluvium consisting of Chaos 

Crags pumice exposed in pit. Sample directly overlies ash cloud deposit related to the upper 

Chaos Crags pyroclastic flow (unit pc, Christiansen and others, 2002). Sample consists of 

charcoalized twigs. Modern rootlets picked out by hand. Sample dates the last major explosive 

phase of the Chaos Crags eruptive sequence. 

USGS 2345 85LP169A 1130 ± 42 

 Charcoal collected from a section of Chaos Crags pyroclastic flows in stream- bank 

exposure on Lost Creek (West Prospect Peak 7-1/2′ quadrangle, 40 ̊ 31.3′ 121 ̊ 28.95′). Sample 

consists of outer 10 rings collected from beneath intact bark on charcoalized log in middle of 

three pyroclastic flows at this locality (unit pc, Christiansen and others, 2002). Chaos Crags 

pyroclastic flows are underlain at this locality by 8-ka debris flow deposits from Lassen Peak 

(unit whe, Christiansen and others, 2002) and overlain by May 1915 debris flows from Lassen 

Peak. Modern rootlets picked out by hand. Sample dates initiation of Chaos Crags eruptive 

sequence. 

USGS 2346 LC85-713 1110 ± 42 

 Charcoal from section of Chaos Crags pyroclastic flows exposed in the south bank of 

Manzanita Creek (Manzanita Lake 7-1/2′ quadrangle, 40 ̊ 31.90′ 121 ̊ 33.15′) near measured 

section 1 of Crandell and others (1974) and at paleomagnetic sample site 4B097 (D.E. 

Champion, personal communication). Sample collected from basal part of the upper Chaos 

Crags pyroclastic flow, which contains abundant, large, conspicuously breadcrusted pumice 

blocks (unit pc, Christiansen and others, 2002). Pyroclastic flow section overlies till. Sample 
9

consists of outer 10 rings from a charcoalized log. Modern rootlets picked out by hand. Sample 

dates last major explosive phase of the Chaos Crags eruptive sequence. See USGS 1614, 1616 

and 2347 from the same locality. 

USGS 2347 LC85-712 1175 ± 42 

 Charcoal from section of Chaos Crags pyroclastic flows exposed in the south wall of 

Manzanita Creek (Manzanita Lake 7-1/2′ quadrangle, 40 ̊ 31.90′ 121 ̊ 33.15′) near measured 

section 1 of Crandell and others (1974) and at paleomagnetic sample site 5B143 (D.E. 

Champion, personal communicationn). Sample collected from basal part of the lower Chaos 

Crags pyroclastic flow (unit pc, Christiansen and others, 2002). This pyroclastic flow directly 

overlies till. Sample consists of small charcoalized branches. Modern rootlets picked out by 

hand and sample cleaned of soil by washing in water. Sample dates initiation of the Chaos Crags 

eruptive sequence. See USGS 1614, 1616 and 2346 from the same locality. 

WW 3286 LC00-2353 1170 ± 40 

 Charcoal from section of Chaos Crags pyroclastic flows exposed in the east bank of 

Manzanita Creek (Manzanita Lake 7-1/2′ quadrangle, 40 ̊ 31.01′ 121 ̊ 32.48′) approximately 1.7 

km upstream from measured section 1 of Crandell and others (1974). Sample collected from 

basal zone of the middle Chaos Crags pyroclastic flow (unit pc, Christiansen and others, 2002). 

Sample consists of an 8-cm-long and 7.5-cm-diameter section of a charcoalized Jeffrey Pine 

branch with bark partially intact. Outer 15 rings peeled off and sparse modern rootlets picked 

out by hand. Sample dates an early phase of the Chaos Crags eruptive sequence. 

WW 3287 LC00-2354 430 ± 30 

Charcoal from hot dome-collapse avalanche deposit approximately 1.0 km ESE of the 

location of measured section 1 of Crandell and others (1974), (Manzanita Lake 7-1/2′

quadrangle, 40 ̊ 31.63′ 121 ̊ 32.35′). Sample collected within the basal zone of the thin edge of 

the dome-collapse avalanche deposit where it overlies the upper Chaos Crags pyroclastic flow, 

which in turn overlies till of Anklin Meadows at this locality. This deposit is interpreted as the 

edge of the hot dome-collapse avalanche from dome D of Chaos Crags by Christiansen and 

others (2002, unit scd). Sample consists of bits of thoroughly charred wood and twigs. Modern 

rootlets picked out by hand and sample washed in water to remove adhering soil. The 

paleomagnetic direction of prismatically jointed juvenile blocks in this deposit agrees with that 

of the older Chaos Crags pyroclastic flows and domes (D.E. Champion, in preparation). Thus, 

the significance of this radiocarbon age is unclear. 

WW 3547 LC01-2365C 710 ± 40 

Charcoal from hot dome-collapse avalanche deposit along the edge of the southernmost 

Sunflower Flat dome, approximately 0.8 km west of Hot Rock on Hwy 89 (West Prospect Peak 

7-1/2′ quadrangle, 40 ̊ 32.12′ 121 ̊ 29.95′). Sample collected within the basal zone of the thin 

edge (about 15 cm thick) of the dome-collapse avalanche deposit where it overlies the upper 

Chaos Crags pyroclastic flow. This deposit is interpreted as the hot dome-collapse avalanche 

from dome east of Chaos Crags by Christiansen and others (2002, unit sce). Sample consists of 

outer parts of a thoroughly charred small branch. Modern rootlets picked out by hand. The 

paleomagnetic direction of prismatically jointed juvenile blocks in this deposit agrees with that 
10

of the older Chaos Crags pyroclastic flows and domes (D.E. Champion, in preparation). Thus, 

the significance of this radiocarbon age is unclear. See WW 3849 from the same deposit. 

WW 3849 LC01-2368 230 ± 40 

Charcoal from hot dome-collapse avalanche deposit along the edge of the southernmost 

Sunflower Flat dome, approximately 1.1 km west of Hot Rock on Hwy 89 (West Prospect Peak 

7-1/2′ quadrangle, 40 ̊ 32.10′ 121 ̊ 30.09′). Sample collected within the thin edge (about 5 cm 

thick) of the dome-collapse avalanche deposit where it overlies the upper Chaos Crags 

pyroclastic flow at this locality. This deposit is interpreted as the hot dome-collapse avalanche 

from dome east of Chaos Crags by Christiansen and others (2002, unit sce). Sample consists of 

bits of throughly charred wood and twigs. Modern rootlets picked out by hand and sample 

washed in water to remove adhering material. The paleomagnetic direction of prismatically 

jointed juvenile blocks in this deposit agrees with that of the older Chaos Crags pyroclastic flows 

and domes (D.E. Champion, in preparation). Thus, the significance of this radiocarbon age is 

unclear. See WW 3547 from the same deposit. 

Other Deposits 

Laboratory number Field number age (yrs B.P.) 

USGS 830 LM79-371 3,310 ± 63 

 Sample collected from landslide in the canyon of Mill Creek (Lassen Peak 7-1/2′

quadrangle, 40 ̊ 24.82′ 121 ̊ 30.90′). Sample collected from trunk of Noble Fir at approximately 

5200’ elevation which is significantly below its normal growth range. The tree trunk was 

transported by a landslide first recognized by Crandell and Mullineaux (1970) that headed on 

Brokeoff Mountain and flowed about 5 km downstream to its present location in Mill Creek. 

Sample collected by M.A. Clynne and L.J.P. Muffler. Sample consists of wood collected from 

just below intact bark. Modern rootlets picked out by hand. Sample dates the youngest large 

landslide in the drainage of Mill Creek and places a constraint on the frequency of large 

landslides in the hyrothermally altered core of Brokeoff Volcano. 

USGS 1352 LC81-730 7,550 ± 58 

Sample collected from canyon exposure in upper Lost Creek, Devastated Area, Lassen 

Peak (West Prospect Peak 7-1/2′ quadrangle, 40 ̊ 30.05′ 121 ̊ 28.86′). Sample consists of thin 

orange-colored soil developed on debris flows comprised primarily of pinkish dacite of Lassen 

Peak (unit whe, Christiansen and others, 2002). Sampled unit overlies dome-collapse pyroclastic 

flow from Lassen Peak dated at 27.1 ka by 40Ar/39Ar (Turrin and others, 1998). Sampled unit 

directly underlies deposits of the 1915 eruption of Lassen Peak. Modern rootlets picked out by 

hand. Sample provides a minimum age for the debris flows from Lassen Peak that are related to 

deglaciation after the early Holocene glacial advance on Lassen Peak (Turrin and others, 1998). 

See USGS 2180. 
11

USGS 1600 82LP28-40 9,360 ± 85 

USGS 1601 82LP28-42 7,760 ± 76 

USGS 1602 82LP28-51 8,045 ± 54 

USGS 1603 82LP28-59 6,820 ± 114 

USGS 1604 82LP28-67 4,390 ± 67 

USGS 1605 82LP28-99 1,275 ± 50 

Samples from a section of intercalated peat and ash in the western creek bank exposed 

just below the Highway 89 bridge over Lost Creek near Anklin Meadows (West Prospect Peak 

7-1/2′ quadrangle, 40 ̊ 32.44′ 121 ̊ 29.52′). Final two digits in sample number indicate height in 

cm above the exposed base of section. Samples from unit 2 of measured section 2 reported by 

Crandell and others (1974). The part of the section from the base to 82LP28-40 consists of 

fluvial sand and gravel. Sample 82LP28-40 was a piece of wood. All other samples consist of 

peat that was thinly sliced to minimize the time span of formation. Modern rootlets picked out of 

all samples by hand, and wood sample washed in water to remove adhering peat. Intervals 

between 82LP28-42 and 82LP28-51, 82LP28-59 and 82LP28-63, and 82LP28-65 and 82LP28-

67 are thin ash beds. Sample 82LP28-99 is from directly beneath fallout pumice at the base of 

the Chaos Crags pyroclastic-flow section. The ash bed above 82LP28-59 is probably Mazama 

Ash. The other two ashes do not correlate with any known eruption from the Lassen area, and 

their sources are unknown. Samples 82LP28-40 and 82LP28-99 are roughly equivalent to W2231 and W-2232 respectively, for which ages of 5,400 ± 600 and 4,600 ± 600 years on bulk 

samples were reported by Crandell and others (1974). Sample 82LP28-99 provides a maximum 

age for the Chaos Crags eruptive sequence. 

USGS 1610 82LP29-150 2,635 ± 58 

Charcoal from soil developed on till beneath Chaos Crags pyroclastic flows exposed in 

the south wall of Manzanita Creek (Manzanita Lake 7 1/2′ quadrangle, 40 ̊ 31.82′ 121 ̊ 33.08′) 

near measured section 1 of Crandell and others (1974). Sample consists of disseminated bits of 

charcoal collected from lower B horizon of soil. Modern rootlets picked out by hand, and 

sample washed in water to remove adhering soil material. Sample dates soil formation and 

provides a maximum age for the Chaos Crags eruptive sequence. See samples USGS 1611 and 

1612 from the same locality. 

USGS 1611 82LP29-312 1840 ± 58 

Charcoal from soil developed on till beneath Chaos Crags pyroclastic flows exposed in 

the south wall of Manzanita Creek (Manzanita Lake 7-1/2′ quadrangle, 40 ̊ 31.82′ 121 ̊ 33.08′) 

near measured section 1 of Crandell and others (1974). Sample consists of disseminated bits of 

charcoal collected from upper B horizon of soil. Modern rootlets picked out by hand, and 

sample washed in water to remove adhering soil material. Sample dates soil formation and 

provides a maximum age for the Chaos Crags eruptive sequence. See samples USGS 1610 and 

1612 from the same locality. 

USGS 1702 82LP32A >42,500 

Sample collected from hornblende-biotite dacite pyroclastic flow widespread in the area 

around Manzanita Lake and Manzanita Creek (Manzanita Lake 7-1/2′ quadrangle, 40 ̊ 32.31′

121 ̊ 34.93′. Unit dated by Crandell and others (1974) as >32,000 years and mapped by 

Christiansen and others (2002) as a pyroclastic flow related to emplacement of Eagle Peak (unit 
12

pfe). This pyroclastic flow is now known to be 66,000 ± 4,000 years old by 40Ar/39Ar dating 

(Christiansen and others, 2002). Sample consists of bits of charcoal picked from ash matrix 

about 15 cm below the top of the ash flow. Modern rootlets picked out by hand, and sample 

washed in water to remove adhering material. Sample provides a minimum age for a major 

silicic eruption that preceded emplacement of Lassen Peak and a control point for calibration of 

U-Th disequilibrium ages reported by Trimble and others (1984). 

USGS 1849 LC83-402 31,280 ± 202 

Peat from section of glaciofluvial sediments exposed in the south bank of the West Fork 

of Hat Creek approximately 500 m east of the Devastated Area parking lot (West Prospect Peak 

7-1/2′ quadrangle, 40 ̊ 30.80′ 121 ̊ 27.62′). Sample from the upper 1 cm of a discontinuous peat 

horizon in glaciofluvial sediments (unit fk, Christiansen and others, 2002) 1 m below fall and 

pyroclastic-flow deposits related to the rhyodacite of Kings Creek (unit pfk). Peat dried and 

modern rootlets removed by hand. Sample provides a maximum age for a major silicic eruption 

that preceded emplacement of Lassen Peak and a control point for calibration of U-Th 

disequilibrium ages reported by Trimble and others (1984). Calibrated age reported by Turrin 

and others (1998). Equivalent to sample USGS 2768. 

USGS 2050 LC81-628 21,990 ± 311 

Sample from an active hot-spring deposit along the Hot Springs Creek Fault near 

Drakesbad (Reading Peak 7-1/2′ quadrangle, 40 ̊ 25.54′ 121 ̊ 24.03′). Sample consists of sinter 

and travertine with some lichen growing on it and probably contained some plant matter 

incorporated into the sinter. As much adhering organic material as possible scraped off. The 

results of this analysis cannot simply be interpreted as an age but indicate that a major 

component of CO2 in the Lassen geothermal system probably has been isolated from the 

atmosphere for 20,000 years or longer. Age calculated with measured δ13C= -4.22 ‰. 

USGS 2061 8-1-E 4,050 ± 76 

 Sample collected from stream cut in mudflow in the canyon of Mill Creek, south of 

Lassen Volcanic National Park (Lassen Peak 7-1/2′ quadrangle, 40 ̊ 24.99′ 121 ̊ 30.98′). 

Sample consists of fragments of charcoal picked from matrix at the base of a >8-m-thick 

mudflow. Modern rootlets picked out by hand, and sample washed in water to remove adhering 

soil material. Sample collected by Donna Marron and Julie Laudon; a preliminary age of 3860 ± 

50 years from it was reported in Marron and Laudon (1986). Sample dates mudflow or landslide 

activity from the hydrotherally altered core of Brokeoff Volcano into the canyon of Mill Creek. 

Probably dates the same deposit as USGS 2063, and may date the same deposit as USGS 830. 

USGS 2063 8-2-F-2 3,940 ± 58 

 Sample collected from stream cut in mudflow in the canyon of Mill Creek, south of 

Lassen Volcanic National Park (Lassen Peak 7-1/2′ quadrangle, 40 ̊ 24.66′ 121 ̊ 30.63′). 

Sample consists of fragments of wood from an organic-rich layer at the base of a >8-m-thick 

mudflow. Modern rootlets picked out by hand, and sample washed in water to remove adhering 

soil material. Sample collected by Donna Marron and Julie Laudon; a preliminary age of 3860 ± 

50 years from it was reported in Marron and Laudon (1986). Sample dates mudflow or landslide 

activity from the hydrotherally altered core of Brokeoff Volcano into the canyon of Mill Creek. 

Probably dates the same deposit as USGS 2061, and may date the same deposit as USGS 830. 
13

USGS 2180 LC85-666 8,130 ± 114 

 Sample collected from canyon exposure in upper Lost Creek, Devastated Area, Lassen 

Peak (West Prospect Peak 7-1/2′ quadrangle, 40 ̊ 30.07′ 121 ̊ 28.82′). Sample consists of 

charcoal picked from soil zone developed on dome-collapse pyroclastic flow from Lassen Peak 

dated at 27.1 ka by 40Ar/39Ar (Turrin and others, 1998). Sample underlies debris-flow deposits 

consisting primarily of pinkish dacite of Lassen Peak (unit whe, Christiansen and others, 2002). 

Modern rootlets picked out by hand, and sample washed in water to remove adhering soil 

material. Sample provides a maximum age for the debris flows from Lassen Peak. Together 

with USGS 1352, sample brackets the age of unit whe between 7,550 ± 55 and 8,130 ± 110 

years. 

USGS 2494 LC86-1011D 34,380 ± 262 

 Sample collected from National Park Service borrow pit near Sunflower Flat (Manzanita 

Lake 7-1/2′ quadrangle, 40 ̊ 33.55′ 121 ̊ 31.93′). Sample consists of a lump of charcoal from 

near the base of near-vent pumice-fall deposit underlying the Sunflower Flat pyroclastic flow 

(unit psf, Christiansen and others, 2002); about 4.5 m below Chaos Crags ash deposits. Modern 

rootlets picked out by hand. Sample dates the initiation of the eruptive sequence that emplaced 

the Sunflower Flat group of domes. 

USGS 2768 LC89-1517 31,700 ± 401 

Peat from section of glaciofluvial sediments exposed in the south wall of the West Fork 

of Hat Creek approximately 500 m east of the Devastated Area parking lot (West Prospect Peak 

7-1/2′ quadrangle, 40 ̊ 30.80′ 121 ̊ 27.62′). Sample from the upper 1 cm of a discontinuous peat 

horizon in glaciofluvial sediments (unit fk, Christiansen and others 2002) 1 m below fall and 

pyroclastic-flow deposits related to the rhyodacite of Kings Creek (unit pfk). Peat dried and 

modern rootlets picked out by hand. Sample provides a maximum age for a major silicic 

eruption that preceded emplacement of Lassen Peak. Calibrated age reported by Turrin and 

others (1998). Equivalent to sample USGS 1849. 

USGS 3534 93CMS110 7,260 ± 58 

 Sample collected from a coquina bed exposed in a trench dug in the 1910s or early 1920s 

for a tunnel outlet along the southeast shore of Eagle Lake (Gallatin Peak 7-1/2′ quadrangle, 40 ̊ 

36.82′ 120 ̊ 43.57′). Sample consists mostly of freshwater snail shells but also contains sparse 

fish teeth and possibly ostracods. The coquina bed rests directly on the vesicular top of a 

subaerial basalt lava flow, which appears to be slightly eroded, probably by wave action along 

the shore of Eagle Lake. Sample collected by M.G. Sawlan. Sample places a minimum age on 

the formation of Eagle Lake and a maximum age of the underlying basalt flow. Age calculated 

with measured δ13C= 1.12 ‰. 

Discussion 

Cinder Cone 

 Cinder Cone consists of a cinder cone, a mostly destroyed older cone remnant, a 

widespread fall deposit, and 5 lava flows in the northeastern corner of Lassen Volcanic National 
14

Park. The age and time span of activity at Cinder Cone has been controversial for over 100 

years. Early workers interpreted it as erupting in the year 1851 (e.g. Finch, 1937). However, a 

variety of stratigraphic and geologic evidence summarized by Clynne and others (2000) indicates 

that all Cinder Cone deposits formed during a single, probably short-lived, eruptive episode. 

Ages reported here for samples dating the Cinder Cone eruption range from 440 to 140 years BP. 

Some of these are minimum ages, and others are maximum ages, as indicated in the sample 

descriptions. Those considered on geologic grounds to date the eruption of Cinder Cone most 

directly are the aspen tree buried by a lava flow (USGS 3684) and the two bark samples from 

beneath the ash layer (USGS 2615 and USGS 3683). The respective ages of these samples are 

255 ± 46, 265 ± 63, and 270 ± 42 years BP. These three samples yield a weighted average of 

264 ± 28 years BP, which is the preferred age for the Cinder Cone eruption (Table 1). Weighted 

averages calculated using all the samples with ages between 200 and 270 years are not 

significantly different from that calculated from the three best samples. Calibration of these 

ages to the radiocarbon timescale yields complex results that are not discussed here. The 

simplest interpretation of these results suggests that Cinder Cone erupted about 1650 A.D. 

(Clynne and others, 2000). 

Table 1. Uncalibrated radiocarbon ages of Cinder Cone deposits. 

Sample 

number

Nature of sample 14C age

yrs BP

Wt mean and std 

error of the mean

USGS 2769 stump in ash 140 ± 42

USGS 3080 log in Snag Lake 200 ± 50

USGS 2665 tree buried by lava flow 200 ± 50

USGS 2493 standing snag in ash 250 ± 46

USGS 3684 aspen buried by lava flow 255 ± 46

USGS 2615 tree bark under ash 265 ± 63

USGS 3683 tree bark under ash 270 ± 42

USGS 3641 log in Snag Lake 270 ± 42

USGS 2664 charcoal from snag on lava flow 405 ± 42

USGS 2663 wood from stump buried in lava 430 ± 50

USGS 2613 wood from standing snag 440 ± 46

3 best samples (USGS 3683, 2615, and 3684) 264 ± 28

5 samples between 250-270 years 262 ± 21

7 samples between 200-270 years 246 ± 18

Chaos Crags

The Chaos Crags comprise a group of six dacite lava domes associated with pyroclastic 

deposits in the northwestern corner of Lassen Volcanic National Park. The radiocarbon data are 

shown in Table 2 and the stratigraphy of the Chaos Crags is summarized in Table 3. Numerous 

radiocarbon ages indicate that the explosive part of the sequence erupted within a short time. 

Three additional radiocarbon ages suggest the possibility that the dome sequence may have taken 

800 years to be emplaced, but interpretation of the youngest dates is uncertain. 
15

The Chaos Crags eruption began with a vent-opening phase followed by explosive 

eruption and emplacement of the lower and middle pyroclastic flows in immediate succession. 

Extrusion of a small lava dome (dome A) and cooling of magma in the conduit then briefly 

plugged the vent. The weighted average age of 9 high-quality radiocarbon samples from the 

lower and middle pyroclastic flows is 1,118 ± 17 years BP. Reopening of the conduit, explosive 

disruption of dome A, and emplacement of the upper pyroclastic flow followed a possible short 

hiatus in the eruptive sequence (Muffler and others 1989). The weighted-average age of 7 highquality radiocarbon samples from the upper pyroclastic flow is 1,083 ± 19 years. The weightedaverage age of all 16 pyroclastic flow samples is 1,103 ± 13 years. Thus, the difference between 

the weighted-average ages of the upper pyroclastic flow and the middle and lower pyroclastic 

flows is small, and its interpretation is uncertain. Interpretation of these ages by calibration to 

calendar years is complicated by the complexity of the radiocarbon calibration curve in the range 

between 900 and 1000 AD. 

Following eruption of the upper pyroclastic flow, domes B through F were emplaced. 

Later, dome C partially collapsed as a series of 3 cold rockfall avalanches that form the Chaos 

Jumbles. The radiocarbon age of the oldest of the avalanches is 278 ± 30 years BP (weighted 

average of 3 samples) comparable to the tree-ring ages of the oldest trees growing on the 

youngest avalanche (Heath 1959). Thus, the data confirm the interpretation of Crandell and 

others (1974) that all three rockfalls occurred in immediate succession. 

Although the relative ages of domes B through F are more or less clear, the time interval 

over which they erupted is not. No radiocarbon or other dates relate directly to domes B, C or F. 

The composition and petrography of dome B more strongly resembles the upper pyroclastic flow 

than the other domes, suggesting that dome B is probably closer in age to the upper pyroclastic 

flow. Evidence concerning the time of emplacement of domes C through F however, is 

conflicting. Small hot collapse events from domes D and E emplaced short-runout lithic 

pyroclastic avalanches (Christiansen and others, 2002). A radiocarbon age of 430 ± 30 was 

obtained from charcoal beneath the pyroclastic avalanche deposit from domes D, radiocarbon 

ages of 710 ± 40 and 230 ± 40 years were obtained from charcoal beneath the pyroclastic 

avalanche deposits from domes E. Dome D was reported to be steaming in the 1850s (Brewer, 

1930), and the petrography and chemistry of the Chaos Crags magma changed subsequent to 

emplacement of dome B. Together these factors suggest that all the post-dome-B units could be 

significantly younger than the upper pyroclastic flow. However, the stratigraphic relationship of 

these radiocarbon samples to their associated avalanche deposit is equivocal. Numerous 

paleomagnetic directional data suggest that all the domes could have been emplaced within a few 

decades of the upper pyroclastic flow at about 1,100 years BP (D.E. Champion, written 

communication, 2002). Furthermore, the radiocarbon samples were collected from the thin 

edges of the avalanche deposits, where the material might have been colluvially reworked. The 

charcoal could represent young forest fires preserved with or beneath colluvium. 
16

Table 2. Uncalibrated radiocarbon ages of Chaos Crags deposits. 

Sample Deposit 14C age

(yrs B.P.)

Wt mean and std

 error of the mean

USGS 1847 Chaos Jumbles 265 ± 42

USGS 1353 Chaos Jumbles 275 ± 63

USGS 1848 Chaos Jumbles 305 ± 58

WW 3849 hot dome collapse avalanche E 230 ± 40

WW 3547 hot dome collapse avalanche E 730 ± 40

WW 3287 hot dome collapse avalanche D 430 ± 30

USGS 2344 upper pyroclastic flow 1,015 ± 42

USGS 2343 upper pyroclastic flow 1,045 ± 42

USGS 1616 upper pyroclastic flow 1,090 ± 54

USGS 2346 upper pyroclastic flow 1,100 ± 42

USGS 1351 upper pyroclastic flow 1,100 ± 67

USGS 1606 upper pyroclastic flow 1,105 ± 58

USGS 1608A upper pyroclastic flow 1,250 ± 67

USGS 1607 upper pyroclastic flow 

(reworked)

1,480 ± 58

USGS 2047 middle pyroclastic flow 1,005 ± 58

USGS 1609B middle pyroclastic flow 1,035 ± 54

WW 3286 middle pyroclastic flow 1,170 ± 40

USGS 2345 lower pyroclastic flow 1,130 ± 42

USGS 1612 lower pyroclastic flow 1,065 ± 58

USGS 1609A lower pyroclastic flow 1,125 ± 54

USGS 2049 lower pyroclastic flow 1,065 ± 58

USGS 1614 lower pyroclastic flow 1,175 ± 54

USGS 2347 lower pyroclastic flow 1,175 ± 42

Chaos Jumbles (n=3) 278 ± 30

upper pyroclastic flow (n=7, all except USGS 1607) 1,083 ± 19

middle and lower pyroclastic flows (n=9) 1,118 ± 17

all pyroclastic flows (n=16, all except USGS 1607) 1,103 ± 13
17

Table 3. Stratigraphy of Chaos Crags after Muffler and others (1989) and Christiansen and others 

(2002) with average uncalibrated radiocarbon ages. 

Event uncalibrated 14C age (yrs B.P.)

Chaos Jumbles–3 cold rockfall avalanches 278 ± 28 B.P. (3)1

Hiatus (?)

Dome F

Hot dome collapse avalanche from dome E 730 ± 40 B.P.2

230 ± 40 B.P.2

Dome E

Hot dome collapse avalanche from dome D 430 ± 42 BP2

Dome D

Dome C (and unnamed dome remnant approximately same 

age)

Hiatus ?

Dome B

Younger pumice cone and upper pyroclastic flow 1,083 ± 19 B.P. (7)1

Dome A (disrupted by eruption of upper pyroclastic flow)

Lower and middle pyroclastic flows

Older pumice cone (mostly buried)

1,118 ± 17 B.P. (9)1

1

 The number in parentheses is the number of radiocarbon dates in the weighted average; 

weighted average of all 16 ages of pyroclastic flows is 1,103 ± 13 BP. 

2

 Significance of these radiocarbon ages is uncertain; see text. 

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18

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