EXP-001 Dirt Project Samples Perris Lake and San Jacinto Mountain

Running on a Rock Cycle: Material Evidence from the SoCal Trifecta Weekend

The Perris Lake Expedition sample set documents a continuous, physically observable progression of granitic material across a single Southern California landscape. Within a relatively small geographic footprint, the samples capture granite at multiple stages of breakdown—from intact bedrock, through mechanical fracturing and differential weathering, to fully mobile sand redistributed at the basin margin.

Taken together, these samples demonstrate that the race course is not merely traversing terrain, but actively crossing different phases of the rock cycle. Elevation, proximity to bedrock, vegetation, and transport mechanisms exert clear control over grain size, sorting, and stability. The result is a landscape where footing, surface behavior, and visual character change abruptly—not due to course design, but due to geology in motion.

This set establishes a baseline framework for the Dirt Project, focusing on process, transition, and context rather than treating samples as isolated specimens. The research methodology used throughout the project is outlined here.

DP-001 Dirt Project Catalog Entry — Granitic Rock Fragment (San Jacinto Mountain)

Sample Type: Granitic rock fragment (quartz-dominant with mafic inclusions)

Location Context: San Jacinto Mountain, near nature center

Proximity: Off-trail, boulder-adjacent

Collection Setting: High-elevation granitic outcrop environment

Material Description

This sample is a small, intact granitic rock fragment composed predominantly of milky-white to translucent quartz, with well-defined dark green to black mafic mineral inclusions embedded within the quartz matrix. The quartz displays interlocking crystalline textures, while the darker minerals appear as angular, discrete patches rather than finely disseminated grains.

Subtle yellow staining along micro-fractures suggests minor iron oxidation, but overall the rock remains relatively fresh.

Grain Shape & Transport History

This fragment shows no evidence of sedimentary transport. Crystal boundaries are sharp and intact, and mineral intergrowth remains undisturbed. The rock likely separated directly from a nearby boulder through:

• mechanical fracturing

• thermal stress (freeze–thaw at elevation)

• root wedging or gravity-assisted detachment

Transport distance is negligible; this is near-source material.

Sorting & Depositional Environment

• Sorting: Not applicable (intact crystalline rock)

• Grain size: Coarse, crystalline, interlocking

• Matrix: Fully lithified

This sample predates soil and sediment formation. It represents exposed bedrock, not a depositional product, and exists outside fluvial or aeolian systems.

Environmental & Course / Terrain Implications

In a mountain environment, material like this manifests as:

• stable boulder fields

• sharp-edged talus fragments

• abrupt transitions between solid rock and loose grus

Footing in these zones is dictated less by sediment mobility and more by fracture geometry and rock spacing.

Process Highlighted

Bedrock exposure and mechanical weathering at elevation

This sample captures granite prior to significant breakdown:

• quartz remains load-bearing and intact

• mafic minerals persist as coherent inclusions

• no rounding, sorting, or redistribution has occurred

It represents the structural source material from which downslope soils and sediments are derived.

Rock Cycle Context

This fragment occupies the earliest observable stage of the local rock cycle:

• intrusive igneous crystallization

• tectonic uplift and exposure

• mechanical fracturing without sedimentary reworking

When compared with Perris Lake beach sand and lower-elevation decomposed granite, it reinforces how elevation and climate slow the transition from rock to soil, preserving crystalline structure longer.

Catalog Note

Collected as part of the ongoing Dirt Project, this San Jacinto Mountain sample serves as a high-elevation reference point for Southern California granitic terrains. It anchors the Dirt Project’s broader narrative by demonstrating how the same parent lithology expresses differently across elevation, moisture, and landscape position.

DP-002 Dirt Project Catalog Entry — Quartz-Rich Decomposed Granite (Near Boulder Zone)

Sample Type: Decomposed granite with quartz clast

Location Context: Off-trail upland zone, downslope from large boulder outcropping

Proximity: Adjacent to previously collected granitic rock fragment

Collection Setting: Transitional slope environment, approximately one mile from major outcrop

Material Description

This sample consists of coarse, poorly sorted decomposed granite containing a prominent milky-white quartz clastembedded within a matrix of angular sand-sized grains. The surrounding material is composed primarily of quartz and feldspar fragments, with scattered dark mineral specks likely representing biotite or hornblende.

The quartz clast remains largely intact and crystalline, while the surrounding matrix shows advanced mechanical breakdown, producing a granular, friable texture.

Grain Shape & Transport History

The quartz clast exhibits minimal rounding, indicating little to no transport from its source. The surrounding granitic matrix is angular to sub-angular, consistent with in-place weathering and very short-distance downslope movement.

Transport mechanisms are limited to:

• gravitational settling

• minor surface wash during precipitation events

• localized disturbance

This material is near-source colluvium, not reworked sediment.

Sorting & Depositional Environment

• Sorting: Poor

• Grain size: Mixed (sand-sized matrix with larger quartz fragment)

• Matrix: Loose, weakly cohesive

The presence of an intact quartz clast within a granular matrix indicates differential weathering, where feldspar-rich components break down faster than more resistant quartz.

This is active material, not stabilized soil.

Environmental & Terrain Implications

From a terrain perspective, this material creates:

• unstable footing under load

• localized collapse around embedded clasts

• sharp transitions between firm and yielding surfaces

Such zones often appear deceptively solid while remaining mechanically unreliable.

Process Highlighted

Differential weathering and early sediment liberation

This sample captures granite mid-transition:

• quartz persists as intact fragments

• feldspar and mafic minerals disaggregate into sand

• material begins to decouple from bedrock without significant transport

It represents the moment where rock becomes sediment, but has not yet been sorted or redistributed.

Rock Cycle Context

This sample occupies a critical intermediate stage in the local rock cycle:

• intact granitic bedrock

• mechanical fracturing and mineral-specific breakdown

• production of decomposed granite and coarse sediment

It sits between the bedrock fragment and the fully mobile sands encountered farther downslope and at the basin margin.

DP-003 Coastal Fringe

Sample Type: Reworked beach sand

Location Context: Shoreline margin, Perris Lake reservoir

Proximity: On-course / immediate course adjacency

Collection Setting: Exposed beach zone, high foot traffic

Grain Shape & Transport History

Unlike upland granitic material, these grains are sub-rounded to rounded, signaling extended transport and repeated abrasion. This rounding is consistent with wave action and shoreline reworking within the reservoir environment.

Although Perris Lake is man-made, the sand reflects a secondary sedimentary cycle:

• original granite weathering upstream

• fluvial transport into the basin

• continuous agitation by wave action and seasonal water-level changes

This sand has been selected, sorted, and refined by motion.

Sorting & Depositional Environment

• Sorting: Moderate to good

• Grain size: Relatively uniform

• Matrix: Loose, non-cohesive

The lack of fines and organic material suggests:

• frequent disturbance

• minimal soil development

• active sediment mobility

This is not soil-forming material—it is persistently reset sediment.

Environmental & Course Implications

From an athlete’s perspective, this sand represents:

• unstable footing

• energy loss with each step

• high variability depending on moisture content

From a geological perspective, it marks the end of one erosion cycle, where material has temporarily come to rest—but remains vulnerable to redistribution.

Process Highlighted

Sedimentary reworking and sorting

This sample contrasts sharply with adjacent upland materials:

• where angular grains record where rock is breaking down

• beach sand records where that breakdown has already been edited by movement

Same parent material. Very different story.

Rock Cycle Context

This sand represents a transitional pause in the rock cycle:

• no longer bedrock

• not yet lithified sedimentary rock

• perpetually in motion

It is geology stripped of memory—only the most durable grains survive repeated transport.

DP-004 Dirt Project Catalog Entry — Upland Granitic Material (Tyrolean Traverse)

Sample Type: Decomposed granite (grus), colluvial

Location Context: Upland slope near Tyrolean Traverse obstacle

Proximity: Off-course, shrub-adjacent

Collection Setting: Lightly vegetated granitic terrain above beach zone

Material Description

This sample consists of poorly sorted, coarse sand to granule-sized material composed primarily of angular quartz and feldspar fragments, with scattered dark mineral inclusions likely representing biotite and hornblende. Grains are irregular in shape and frequently occur as loosely bound micro-aggregates rather than discrete particles.

The overall coloration is pale yellow to tan, with localized darker flecking, reflecting incipient iron oxidation and minimal organic staining.

Grain Shape & Transport History

Grains are predominantly angular to sub-angular, indicating minimal transport from their parent rock. Unlike beach sand, this material has not undergone sustained abrasion or sorting. Fragment edges remain sharp, preserving the fracture geometry of the original granite.

Transport is dominated by:

• in-place weathering

• short-distance downslope movement

• limited wind redistribution

This material remains geologically local.

Sorting & Depositional Environment

• Sorting: Poor

• Grain size: Highly variable

• Matrix: Weakly cohesive due to fine material and minor organic content

The presence of loosely bound aggregates suggests:

• intermittent moisture retention

• early soil-forming processes

• influence from nearby vegetation

This is not stable soil, but soil in formation.

Environmental & Course Implications

From an athlete’s perspective, this material produces:

• variable traction

• unexpected surface collapse

• inconsistent footing near obstacles and traverses

From a geological perspective, it represents a transition zone between intact bedrock and mobile sediment, where landscape evolution is actively underway.

Process Highlighted

Mechanical weathering and early soil development

This material captures granite in the act of disintegration:

• feldspar breaking down

• quartz persisting

• fines accumulating locally rather than being removed

It records where erosion begins, not where it ends.

Rock Cycle Context

This sample occupies an early stage in the sedimentary pathway:

• bedrock → decomposed granite → colluvial sediment

Unlike beach sand, which reflects repeated recycling, this material preserves first-generation breakdown directly from its parent lithology.

DP=005 Dirt Project Catalog Entry — Granitic Rock Fragment (Upland Boulder Zone

Sample Type: Granitic rock fragment (quartz-dominant with mafic inclusions)

Location Context: Upland trail margin near large boulder outcropping

Proximity: Off-course, immediate trail adjacency

Collection Setting: Bedrock-proximal zone at approximately mile 7

Material Description

This sample is a small, intact granitic rock fragment composed primarily of massive, milky-white quartz, with embedded dark green to black mafic mineral inclusions. The quartz matrix appears crystalline and interlocking, while the darker minerals occur as discrete, irregular patches rather than disseminated grains.

Surface textures suggest minimal weathering, with fracture planes and mineral boundaries remaining clearly defined.

Grain Shape & Transport History

Unlike the previously cataloged sand and decomposed granite, this sample shows no evidence of sedimentary transport. Mineral boundaries are sharp, and crystal intergrowth remains intact, indicating the fragment separated directly from a nearby bedrock source.

Transport history is limited to:

• in-place fracturing

• short-distance gravitational movement

• possible thermal or mechanical stress-induced detachment

This rock is essentially in situ, representing source material rather than derived sediment.

Sorting & Depositional Environment

• Sorting: Not applicable (intact rock fragment)

• Grain size: Crystalline, interlocking

• Matrix: Solid, lithified

This sample predates soil and sediment formation entirely. It occupies the bedrock end-member of the local geological system and exists outside normal depositional processes.

Environmental & Course Implications

From an athlete’s perspective, this material manifests as:

• large, stable boulders

• abrupt footing transitions

• obstacle anchor points and visual landmarks

From a geological perspective, these outcrops represent the structural framework of the course—the immobile elements from which all surrounding loose material is ultimately derived.

Process Highlighted

Bedrock exposure and mechanical fracturing

This sample captures granite before disintegration:

• quartz remains intact and load-bearing

• mafic minerals persist as inclusions

• no sorting, rounding, or redistribution has occurred

It represents the starting point of the erosion sequence documented elsewhere on the course.

Rock Cycle Context

This fragment occupies the earliest observable stage of the local rock cycle:

• crystallized intrusive igneous rock

• uplift and exposure

• incipient fracture without sedimentary reworking

When paired with nearby decomposed granite and beach sand samples, it completes a continuous sequence:bedrock → grus → sand

Dirt Project Highlights — EXP-001 Sample Set

DP ID	Sample Context	Material Type	Key Characteristics	Process Highlighted	Rock Cycle Position
DP-001	San Jacinto Mountain, near boulder outcrop	Intact granitic rock fragment	Interlocking quartz crystals; dark mafic inclusions; minimal weathering	Bedrock exposure & mechanical fracturing	Source rock (igneous bedrock)
DP-002	Upland trail margin near boulder (Perris area)	Granitic rock fragment	Quartz-dominant matrix; sharp mineral boundaries; no transport	Initial detachment from bedrock	Early breakdown stage
DP-003	Downslope from boulder outcrop	Decomposed granite with quartz clast	Angular grains; intact quartz fragment; poor sorting	Differential weathering	Rock → sediment transition
DP-004	Shrub-adjacent upland slope (Tyrolean Traverse area)	Decomposed granite (grus)	Angular grains; weak aggregation; minor organic influence	Mechanical weathering & early soil formation	Colluvial sediment
DP-005	Perris Lake shoreline	Reworked beach sand	Rounded grains; good sorting; loose, mobile sediment	Sedimentary reworking & sorting	Basin sediment (temporary sink)

References

Granite, Igneous Processes, and Mineral Composition

Winter, J. D. (2010). Principles of igneous and metamorphic petrology (2nd ed.). Pearson Education.

Nesse, W. D. (2012). Introduction to mineralogy (2nd ed.). Oxford University Press.

Weathering, Decomposed Granite, and Grus Formation

Birkeland, P. W. (1999). Soils and geomorphology (3rd ed.). Oxford University Press.

Brady, N. C., & Weil, R. R. (2016). The nature and properties of soils (15th ed.). Pearson.

Hillslope Processes, Colluvium, and Near-Source Sediment

Selby, M. J. (1993). Earth’s changing surface: An introduction to geomorphology (2nd ed.). Oxford University Press.

Summerfield, M. A. (1991). Global geomorphology. Longman Scientific & Technical.

Sediment Transport, Sorting, and Basin Deposition

Boggs, S. (2011). Principles of sedimentology and stratigraphy (5th ed.). Pearson.ts.

Nichols, G. (2009). Sedimentology and stratigraphy (2nd ed.). Wiley-Blackwell.

Rock & Mineral Identification Apps (iPhone)

Rockd – Rock & Mineral Identifier. (2025). Mining Apps LLC. (Mobile app) [iPhone]. App Store. https://apps.apple.com