Geology and Topographic Mapping Essentials

Flashcards covering geologic laws of relative dating, unconformities, structural geology, topography, stream dynamics, and groundwater principles.

Law of Superposition

The law that governs the order of rock sequences, stating that the oldest rocks fall at the bottom of the sequence.

Original Horizontality

The law governing the original orientation of rocks in a sequence, suggesting they are deposited flat.

Lateral Continuity

The law governing the extent to which rocks are originally deposited in all directions.

Law of Inclusions

The law stating that a rock containing an inclusion of another rock is younger than the rock the inclusion came from.

Cross-cutting Relationships

The law stating that a rock or fault cutting through another rock is younger than the rock it cuts across.

Unconformities

The principle governing gaps in geologic time that occur when rocks are eroded or not deposited.

Disconformity

A specific type of unconformity that occurs when horizontal sedimentary rocks are eroded and then more sedimentary rocks are deposited on top.

Nonconformity

An unconformity that occurs when igneous or metamorphic rocks are eroded and then sedimentary rocks are deposited on top.

Angular Unconformity

An unconformity that occurs when folded rock layers are eroded and then sedimentary rocks are deposited on top.

Index Fossil

A fossil used to identify specific time periods in the rock record.

Geologic Map Key Arrangement

The convention where the oldest rocks are placed at the bottom of the map key, and youngest at the top.

Normal Fault

A fault type that forms from extensional forces.

Reverse Fault

A fault type that forms from compressional forces.

Anticline

An A-shaped fold where the oldest rocks are located in the center.

Syncline

A U-shaped fold where the youngest rocks are located in the middle.

Dome

A 360-degree bullseye structure with the oldest rocks in the center.

Basin

A 360-degree bullseye structure with the youngest rocks in the middle and strike and dip symbols pointing toward the center.

Formation Symbol

A code where the first letter corresponds to the first letter of its geologic time period.

"T" Symbol

A map symbol used to indicate the strike and dip of rocks.

Dip Direction

The rule that older rocks always dip towards younger rocks.

Contour V-shape

A pattern in contour lines that points upstream.

Topographic Gradient

$\text{Gradient} = \frac{\text{Difference in elevation}}{\text{Distance}}$; for example, two points $5\text{ mi}$ apart with elevations of $1200\text{ ft}$ and $1000\text{ ft}$ have a gradient of $40\text{ ft/mi}$.

Contour Spacing

Closely spaced lines indicate steep slopes, while far spaced lines indicate flat slopes.

Contours

Lines on a topographic map that represent areas of equal elevation.

Relief

The calculated difference between the high point and low point on a map ($\text{Relief} = \text{High point} - \text{Low point}$).

Ratio Scale

A numerical scale representation such as 1:24,000.

Verbal Scale

A scale expressed in words, such as 1 inch = 2,000 feet.

Benchmark

A designated metal plate on a map identified by an elevation, a big "X", and the letters "BM".

Braided Stream System

A stream system characterized by a high sediment load.

Meandering Stream System

A stream system characterized by a low sediment load.

Young Stream System

Features of this system include straight channels, rapids, and no floodplain.

Point Bar

The location in a meandering stream where deposition occurs.

Cut Bank

The location in a meandering stream where erosion occurs and velocity is fastest.

Dendritic Drainage

A drainage pattern that resembles the branching of a tree.

Hydraulic Gradient

For wells $10\text{ m}$ apart with heads of $150\text{ ft}$ and $200\text{ ft}$, the gradient is $5\text{ ft/m}$.

Potentiometric Surface

The level to which hydraulic head is equal in a confined aquifer.

Water Table

The level to which hydraulic head is equal in an unconfined aquifer.

Aquifer

An underground layer of rock with high porosity and high permeability where groundwater is stored and can flow.

Saturated Zone

The portion of an aquifer where the pore spaces are completely full of water.

Unsaturated Zone

The portion of an aquifer where the pore spaces are full of air.

Arid Weathering and Erosion

In deserts, mechanical weathering is dominant, and these processes occur more slowly than in humid environments.

Ridge-formers

Rock types such as limestone and sandstone that are resistant to erosion in arid environments.

Slope-formers

Rock types such as shale and mudstone in arid environments.

Parabolic Dune

A dune shaped like a crescent moon with the horns pointing upwind, opposite to the direction of wind flow.