*Arkansas Valley Bouldering South

33 boulder problems · granite · 7,679 ft

Help locate these routes: survey the wall

What's here

V0 to V10, mostly around V0.

9 V0
4 V1
7 V2
4 V3
2 V4
1 V5
2 V6
2 V7
1 V8
1 V10

Counted from the 33 climbs here that carry a grade. Shown only where there are at least 5 of them — below that the shape is noise.

How well located

Base placed (one source) 5 Position on wall known 23 Crag only 5

The order of the climbs along this wall is known from the open catalogue, so a few surveys go a long way: standing at The Junction, Slab Dyno Project (2 climbs, about 60 seconds on Hecla Junction North) would place up to 3 more climbs between them. Survey the wall →

“Up to” because the estimate between two surveyed routes is only used when they turn out to be close enough together on the ground.

Rock, from the geologic map

Topaz rhyolite flow of Nathrop Volcanics, including basal vitrophyre. Rupelian, about 34 to 28 million years old.

Light-gray, light pinkish-gray, and purplish-gray, strongly flow-layered alkaline rhyolite flow forming prominent outcrops, about 8 km south-southeast of Buena Vista at Ruby Mountain, Sugarloaf Mountain, and upper part of Bald Mountain (Keller and others, 2004). Layering is moderately to strongly folded. The rhyolite consists of small, sparse phenocrysts of smoky quartz, sanidine, plagioclase, and rare biotite in a dense microcrystalline groundmass; accessory minerals are apatite, zircon, magnetite, garnet, and topaz (Keller and others, 2004). Locally contains spherules as much as 10 cm in diameter, and lithophysae as much as 6 cm in diameter, particularly on Bald Mountain. Lithophysal cavities locally contain euhedral crystals of spessar- tine garnet and topaz, some of gem quality (Voynick, 1994). The basal vitrophyre is glassy, composed mostly of light-gray, brownish-gray, or black perlite with subordinate pitchstone. The perlite typically shows an “onion-skin” structure. One 40Ar/39Ar age on plagioclase on Bald Mountain is 29.25±0.12 Ma, and three 40Ar/39Ar ages on sanidine at Ruby Mountain are 30.47±0.08 29.25±0.21Ma, and 30.74±0.08 Ma (McIntosh and Chapin, 2004; ages corrected for revised standards of Kuiper and others, 2008), indicating early Oligocene age (McIntosh and Chapin, 2004). Similarity of age and composition (for example, presence of accessory topaz) with evolved Mount Antero leucogranites suite of Sawatch Range suggests genetic connection (Shannon, 1988). On Bald Mountain, the rhyolite is estimated to be about 150 m thick and was depos- ited within a paleovalley that also contains remnants of older Wall Mountain Tuff and Tallahassee Creek Conglomerate (Keller and others, 2004)

This is the map unit under this crag's map point, read from the 1:100,000 sheet (Kellogg and others, 2017, U.S. Geological Survey Scientific Investigations Map 3382). The point can be a few hundred metres from the rock, a cliff often stands on the line between two units, and at that scale a line on the map is about 100 m wide on the ground, so the wall itself may be the neighbouring unit. The rock named at the top of this page comes from the public geology of this area; this card is the map's answer. Every crag on this unit: Topaz rhyolite flow of Nathrop Volcanics, including basal vitrophyre. Geology data: Macrostrat (CC BY 4.0), serving USGS and Colorado Geological Survey maps.

On the map since 1955

The USGS has mapped this ground since 1955. 20 historical sheets cover this crag's map point; the oldest is below.

Thumbnail of the 1955 USGS sheet covering *Arkansas Valley Bouldering South — **USGS 1:62500-scale Quadrangle for Buena Vista, CO 1955** · U.S. Geological Survey · 1955 · 1:62,500 sheet
USGS Historical Topographic Map Collection · Public domain · the record · placed by its coordinates

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Hidden as soon as you tell us, everywhere it appears, before anyone reviews it.

Public domain, U.S. Geological Survey. The sheet shows the ground as the survey found it then, which is why a trail or road you know may be missing. Every sheet over this point, 1955 to 1994: USGS topoView.

From the archives

Photographs of this area held by the Library of Congress, oldest first. Every one carries the Library's own "no known restrictions on publication"; anything else is left out.

High bridge near Buena Vista · Jackson, William Henry, 1843-1942 · 1880
Library of Congress, Prints & Photographs Division · Public domain · the record · indexed to this place by the archive

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