CPG Geologic Mapping & Field Techniques 2

Question 1

A bed is recorded as striking N30E and dipping 40° to the SE. What is the dip direction azimuth?

Accepted Answer

120°

Answer

Dip direction is perpendicular to strike on the down-dip side, so N30E + 90° to the SE gives 120°.

Question 2

Beds dip downstream at an angle steeper than the stream gradient. Which way does the outcrop V point where the beds cross the valley?

Accepted Answer

Downstream

Answer

Under the rule of Vs, beds dipping downstream more steeply than the stream gradient form Vs that point downstream.

Question 3

A cross-section is drawn at an oblique angle to strike. How does the dip shown on the section compare with the true dip?

Accepted Answer

It is less than the true dip

Answer

Apparent dip on any section not perpendicular to strike is less than the true dip.

Question 4

Local magnetic declination is 12° E. A Brunton without a declination correction reads a magnetic bearing of 050°. What is the true bearing?

Accepted Answer

062°

Answer

With east declination, you add it to the magnetic bearing to get the true bearing: 050° + 12° = 062°.

Question 5

On a standard USGS-style geologic map, what does a dashed contact line usually mean?

Accepted Answer

An approximately located contact

Answer

Solid lines mark accurately located contacts, dashed lines mark approximately located ones, and dotted lines mark concealed ones.

CPG - Certified Professional Geologist Practice Test