UNITED STATES DEPARTMENT OF THE INTERIOR 

GEOLOGICAL SURVEY

Geologic Map of the Lund Ouadrangle, 

Iron County, Utah

By 

S. Kerry Grant and Myron G. Best

Open-File Report 79-1655 

1979

This report is preliminary and has not been

edited or reviewed for conformity with U.S.

Geological Survey standards.
DESCRIPTION OF MAP UNITS

ALLUVIUM AND COLLUVIUM (QUATERNARY) Unconsolidated, poorly 

sorted stream, fan, slope-wash, and playa deposits of 

gravel, sand, silt, and clay; includes small exposures of 

older alluvium. Less than 100 m thick on the eastern flank 

of the range, but thickens beneath the Escalante Desert

ALLUVIUM AND LAVAS (PLEISTOCENE, PLIOCENE, AND MIOCENE) Weakly 

consolidated, pale-orange-gray sandstone and pebble to 

boulder conglomerate of alluvial origin, and flows and 

feeder dikes of medium-gray olivine basalt(?) and dark 

brown-gray rhyodacite. Clasts in the conglomerate are dark 

volcanic rock and a variety of Mesozoic and Paleozoic 

sedimentary rocks. Thickness at least 150 m

FORMATION OF RLAWN WASH (MIOCENE) Chiefly rhyolite tuffs and 

lava flows named for exposures near Blawn Wash northwest of 

the Lund Quadrangle

Tuff member Pink to pale-yellow and orange, weakly to 

moderately welded lithic ash-flow tuffs. At Broze Knoll 

the upper part of the member consists of at least two tuffs 

of differing lithic content. The upper tuff contains 

abundant lithic fragments as large as 10 cm in diameter of 

brown-gray flow-foliated rhyolite containing sanidine, 

plagioclase, and biotite. A sandstone unit of possible 

base-surge origin, less than one meter thick separates the 

upper tuff from an underlying tuff that contains only a few 

percent lithic fragments. Both tuffs contain 10-15 percent 

phenocrysts of plagioclase, sanidine, quartz, biotite, and 

a trace of sphene. The tuffs at Broze Knoll are a 

25 m-thick sequence of epiclastic volcanic sediments 

filling a channel cut into the underlying tuff of Leigh 

Well. The upper half of this sequence consists of 

interbedded cream-colored sandstone and siltstone with 

minor pumice-rich conglomerate; the lower half is a tan 

pebble conglomerate with brown, red, and green volcanic 

clasts. Total thickness of the unit is more than 100 m

TUFF OF LEIGH WELL (MIOCENE) Rust, pale-orange to pink,

moderately to weakly welded, ledge-forming ash-flow tuff. 

A dark olive-gray basal vitrophyre contains abundant lithic 

fragments as much as 8 cm long of dark volcanic rocks 

including hornblende andesite of the unit Tha. Phenocrysts 

comprise 10-20 percent of the tuff with plagioclase 

predominating in the lower half of the unit and sanidine 

more abundant near the top; biotite is present 

throughout. Thickness on the west flank of Broze Knoll is 

20 m but the unit thins westward where it is included 

within the unit Tbt

HORNBLENDE ANDESITE FLOW (OLIGOCENE) Reddish-gray flowfoliated lava with conspicuous needles of hornblende. At 

least 100 m thick
ISOM FORMATION (OLIGOCENE) Red and purple densely welded

vitric ash-flow tuffs and a lava flow. Tuffs contain 5-10 

percent phenocrysts of plagioclase and traces of altered 

pyroxene. The lava flow has a hasal hlack vitrophyre and 

contains larger and more abundant phenocrysts of 

plagioclase and pyroxene. Stretched vesicles are alined 

between N., 40° W. and N. 70° W. Collapsed pumice lapilli 

in the tuffs are generally porous; in one of the lower 

tuffs vesicles or pumice voids have been completely filled 

with calcite and other milky white secondary minerals. 

Matrix of the tuffs and lava flow ranges from massive to 

strongly foliated with flow folds common. Unit weathers to 

plates and grus. Thickness ranges from 100 m in the north 

to more than 150 m in the south. Age, 25 m.y. (Fleck and 

others, 1Q75)

NEEDLES RANGE FORMATION (OLIGOCENE) Sheets of densely to 

moderately welded, crystal-rich ash-flow tuffs. The 

Needles Range can be divided into mappable parts over most 

of its extent, and should be assigned to higher 

stratigraphic rank. Age, 29 m.y. (Fleck and others, 1975) 

Lund Tuff Member A single cooling unit 300-400 m thick of 

red, brown, to pink tuff containing 30-45 percent 

phenocrysts of mainly plagioclase, with lesser quartz and 

biotite, inconspicuous hornblende, and traces of sanidine, 

sphene, and pyroxene. The quartz is conspicuous and ranges 

widely in abundance and size, but a few grains larger than 

2 mm diameter are present almost everywhere. Pumice is 

most distinct toward the top of the unit where a few brown 

lithic fragments also occur. Plagioclase and hornblende 

are slightly more abundant in the middle third of the 

unit. A basal vitrophyre is exposed only in the northwest 

part of the quadrangle. Included in the unit below the 

tuff is an underlying complex of gray crystal-poor ash-flow 

tuff, volcanic sandstone interbedded with the tuff, and 

dark-brown lavas of intermediate composition; this complex 

is thickest in the southern part of the quadrangle where it 

approaches 100 m

Wah Wah Springs Tuff Member (Oligocene) A single cooling 

unit of ash-flow that ranges from light gray at the top to 

red at the base and contains 25-50 percent phenocrysts of 

mainly plagioclase, with lesser hornblende and biotite, 

inconspicuous quartz, and a trace of pyroxene. The top of 

the cooling unit has the least crystals and the middle the 

most. Hornblende is nearly absent from the uppermost tuff 

which has small dark lithic fragments. Ouartz grains do 

not exceed 2 mm in diameter. Vitrophyre is present at the 

base. A three-meter bleached and fractured zone occurs 

near the middle of the unit in the south. Total thickness 

ranges from 250 m in the south to 120 m in the north where 

it overlies the rhyolite unit (Ter)
ESCALANTE DESERT FORMATION (OLIGOCENE)--Unit named by Grant 

(1978)

Rhyolite member Striped red and light-gray flow-foliated 

rhyolite containing 5 percent phenocrysts of chalky 

feldspar and minor hornblende and biotite. Isoclinally 

flow folded in the upper half with gently inclined 

north-south axes on folds of eastward vergence and steep 

east-west axes and axial planes on another set. Flow 

layers are parallel to the base of the flow in the lower 

half. Flow breccia occurs at the base. Almost 200 m thick

Andesite flow and dikes member Dark-gray, massive to

vesicular lava flow as much as 50 m thick with fine-grained 

phenocrysts of plagioclase and pyroxene. Dark-gray, weakly 

resistant dikes are 5-15 m wide between ribs of resistant 

baked host rock; ranges from massive aphanitic to vesicular 

with calcite filling elongate tubular cavities

Tuff member Sequence of crystal-poor lithic-rich ash-flow 

tuffs and minor volcaniclastic deposits. The uppermost 

tuff cooling unit has 9-19 percent phenocrysts mainly of 

plagioclase with some hornblende and biotite; volcanic 

fragments constitute 5-10 percent of this unit with the 

higher concentrations at the base; the color ranges from 

pink-gray at the top through red-brown to black in a basal 

vitrophyre; thickness is 21 m in sec. 6, T. 32 S., R. 14 W., 

but it is absent where the rhyolite member (Ter) is 

thick. The underlying tuff cooling unit is lithologically 

similar, but is thicker (87 m), has traces of quartz and 

sanidine, has an orange basal vitrophyre with considerable 

red-gray moderately welded tuff below the vitrophyre, and 

hornblende is confined to the vitrophyre and the tuff below 

it; this tuff is also thin to absent in the vicinity of the 

rhyolite member (Ter).

Older tuffs in the sequence have only 2-6 percent 

phenocrysts of plagioclase and quartz and a trace of 

biotite. From the top down these tuffs are pink gray to 

light orange brown, light gray and green gray. They have 

as much as 12 percent lithic fragments which are more 

abundant at the base and increase in size to as much as 

6 cm across toward Marsden Spring where they are of 

volcanic rock and pink, red, and purple quartzite and green 

phyllite. Thickness is 78 m in the southeast, increasing 

westward to more than 150 m at Marsden Spring.

A basal tuff, about 10 m thick, occurs in the north 

half of the quadrangle; it is red-purple to gray and has as 

much as 20 percent crystals of plagioclase, quartz, and 

biotite.

Volcaniclastic beds occur between the ash-flow sheets 

and decrease in thickness and size of clasts downward in 

the unit; the top bed is 20 m thick and consists of 

volcanic conglomerate with boulders approaching two meters 

in diameter. The basal bed consists of reversely graded 

volcanic sandstone 6 cm thick
ASH-FLOW TUFF (OLIGOCENE)--Green, red, and gray densely welded 

but weakly resistant tuff with 25-30 percent phenocrysts of 

plagioclase and quartz, minor biotite, and traces of 

sanidine and hornblende. Ouartz is in large grains more 

than 3 mm in diameter that are locally euhedral in pumice 

fragments; biotite is warped and conspicuous even where the 

flakes are as little as 0.1 mm across. Sheeting fractures 

along or at a low angle to the compaction foliation are 

pervasive. Lithic fragments as large as 15 cm across occur 

at the base and include a quartz-rich volcanic rock and 

some carbonate rocks. As much as 200 m thick in places, 

but absent in the south

CONGLOMERATE (OLIGOCENE, EOCENE OR PALEOCENE) Red to brown, 

weakly resistant cobble to boulder conglomerate. Clasts 

and matrix are predominantly of volcanic rocks with sparse 

poorly exposed lava flows at the top, through quartzites in 

the middle, to predominantly carbonate rocks at the base; 

clasts are as large as 1 m in diameter, but are generally 

much smaller. Thickness ranges from a few tens of meters 

to as much as 150 m

NAVAJO SANDSTONE (LOWER JURASSIC AND UPPER TRIASSIC) The upper 

part is a resistant, uniform, red sandstone with 

concretions 2 cm in diameter and large-scale crossbeds that 

suggest a source to the northwest; partially silicified 

where cut by a thrust fault. The lower part is coarse 

cross-laminated sandstone and pebble conglomerate 10-20 m 

thick, possibly equivalent to the Shinarump Conglomerate. 

Poorly exposed red siltstone between the upper and lower 

parts of the unit may be equivalent to the Chinle 

Formation. Overall thickness of the unit exceeds 500 m

CAMBRIAN CARBONATE ROCKS, UNDIVIDED (MIDDLE(?) CAMBRIAN) 

Moderately resistant, mottled dark and light gray or slate 

gray and buff carbonate. Occurs in one large outcrop near 

Marsden Spring where it is in thrust fault contact with 

underlying Mesozoic sandstone
EXPLANATION OF SYMBOLS

 --- CONTACT Dashed where inferred or approximately located

D 

_. -i_». FAULT Dashed where inferred or schematically located; dotted

where concealed. Ball and bar, or D, on downthrown side

-TTTTTT LOW-ANGLE DENUDATION FAULT Teeth on upper plate 

' * * * THRUST FAULT Teeth on upper plate 

.is STRIKE AND DIP OF BEDDING 

^ STRIKE AND DIP OF COMPACTION FOLIATION IN ASH-FLOW TUFFS

STRIKE AND DIP OF FLOW LAYERING IN LAVAS AND REMOBILIZED TUFFS 

^ Inclined 

Vertical 

-«- EROSIONAL SCARP Probably an ancient lake shoreline
REFERENCES

Best, M. G., Shuey, R. T., Caskey, C. F., and Grant, S. K., 1973,

Stratigraphic relations of members of the Needles Range Formation

at type localities in southwestern Utah: Geological Society of

America Bulletin, v. 84, p. 3269-3278. 

Campbell, D. R., 1978, Stratigraphy of pre-Needles Range Formation

ash-flow tuffs in the northern Needle Range and southern Wah Wah

Mountains, Beaver County, Utah: Brigham Young University Geology

Studies, v. 25, p. 31-46. 

Dinkel, T. R., 1969, Vertical and lateral variations in a welded tuff:

Rolla, University of Missouri, unpublished M.S. thesis, 58 p. 

Fleck, R. J., Anderson, J. J., and Rowley, P. D., 1975, Chronology of

mid-Tertiary volcanism in High Plateaus region of Utah: Geological

Society of America Special Paper 160, p. 53-61. 

Grant, S. K., 1978, Stratigraphic relations of the Escalante Desert

Formation near Lund, Utah: Brigham Young University Geology

Studies, v. 25, p. 27-30. 

Kreider, J. E., 1970, The Lund ash-flow tuff: Rolla, University of

Missouri, unpublished M.S. thesis, 73 p. 

Miller, G. M., 1966, Structure and stratigraphy of southern part of

Wah Wah Mountains, southwest Utah: American Association of

Petroleum Geologists Bulletin, v. 50, p. 858-900.