Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

The larger and more interesting caves
along this tube system are shown on
maps 10, 11 , and 12 of plate 4 and
described in previous sections on Bearpaw,
Merrill Ice, Kirk Whites, Beaconlight,
and particularly Skull Caves.
Therefore, associated surface featuresthe
breakdowns, sag basins, skylights,
surface spillovers, and various kinds of
hydraulic ramparts that surround or partly
border some of the collapse trenchesare
shown on map 20, plate 6. It shows
the surface features along a 5-mi stretch
extending downstream from the collapse
trench at the head of Skull Cave. This
part of the lava-tube system zigzags
along in a broad curve around the older
Schonchin Butte flow (fig. 70). Near the
north end of the Schonchin Butte flow,
many distributaries branch off to the
north and are lost in a field of schollendomes
that occupy a broad band within
the monument between Captain Jacks
Stronghold and Fern Cave.
Skull Breakdown to
Captain Jacks Bridge
A large collapse trench gives entrance
to Skull Cave. Vehicles can be left
at the Skull Cave parking lot. From this
point the unpaved part of Lyons Road
(now abandoned and closed to all vehicular
traffic because it is within a wilderness
area) furnishes a good access trail,
which lies close to the lava-tube system
for the first 2.5 mi.
Skull Cave breakdown is one of the
largest and deepest collapse trenches in
the monument. Cliffed walls around its
edge provide excellent exposures of flow
units within a thick lava flow. From the
base of these cliffs long talus piles of
very coarse blocks merge into an irregular
and hummocky sea of tumbled
blocks of all sizes. Looking downstream
into the entrance of Skull Cave (fig. 47),
one is startled by its thin roof and the
realization that it is only a matter of time
until the collapse trench will extend
throughout the entire length of Skull
Cave.
The next collapse feature downstream
is offset 600 ft southeast from a
point on the surface that lies above the
downstream end of Skull Cave. It is a
roughly circular shallow depression
about 300 ft in diameter, located on the
south side of Lyons Road. Parts of it are
so overgrown with brush that it is difficult
to tell whether this feature is merely
a sag basin with gently tilted edges or
whether its margins were let down by
small displacements along numerous arcuate
faults. Near its center is a small pit
that is surely the surface expression of
collapse into an underlying lava tube.
Just east of the rim of this basin lies a
deep collapse hole that reveals a tiny
remnant of the lava tube at its base.
Another deep collapse, 350ft to the east,
opens up another two short sections of
lava tube that J.D. Howard named Robin
Figure 69. Edge of Callahan flow near Whitney Butte, west side of Lava Beds National Monument. Flow front of block lava
is about 30ft high. Callahan flow is about 1,100 years old, youngest in the monument.
96 Selected Caves and Lava-Tube Systems, Lava Beds National Monument, California