Earth Science Quiz: Field Observations

20 questions · exam conditions

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Field ObservationsQuestion 1 of 20

A geologist is mapping a large area with consistent regional tilting of sedimentary rocks. She finds a road cut that exposes the layers, but the vertical face of the cut is oriented at a 45° angle to the strike direction. The inclination angle she measures on this exposed face will be:

equal to the true dip angle.

greater than the true dip angle.

less than the true dip angle.

equal to the strike azimuth.

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Earth Science Quiz

Earth Science Quiz: Field Observations

Practice Field Observations in Earth Science with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Field Observations, giving you a quick way to practice the rules, question types, and explanations that matter most for Earth Science.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

equal to the true dip angle.
greater than the true dip angle.
less than the true dip angle. (correct answer)
equal to the strike azimuth.

Explanation: The true dip is the maximum angle of inclination, measured on a vertical plane that is perpendicular to the strike. Any vertical plane that is not perpendicular to the strike will show an 'apparent dip' which is always less than the true dip. Since the road cut is at 45° to the strike, it is not perpendicular, and thus the measured angle will be an apparent dip, which is less than the true dip.

Question 2

A road cut oriented perfectly East-West exposes a bedding plane that has a true dip of 30° directly to the South. What will be the angle of the trace of this bedding plane as seen on the vertical face of the road cut?

Exactly 30°
Exactly 0° (horizontal) (correct answer)
Greater than 30°
Less than 30° but greater than 0°

Explanation: The true dip is to the South, which means the dip direction is 180°. The strike is perpendicular to the dip direction, so the strike must be East-West (090°/270°). The road cut is also oriented East-West, meaning it is parallel to the strike of the bedding plane. A vertical cross-section cut parallel to the strike will show the trace of the dipping plane as a horizontal line (0° inclination).

Question 3

A geologist observes a hillside where the ground surface is parallel to the underlying sedimentary beds, forming a 'dip slope'. The strike of the beds is known to be N-S. The geologist measures the slope of the ground surface and finds it descends 15° towards the East. What is the correct strike and dip of the bedding?

Strike N-S, Dip 15° W
Strike E-W, Dip 15° E
Strike N-S, Dip 15° E (correct answer)
Strike N-S, Dip cannot be determined from this information.

Explanation: A 'dip slope' is a geomorphological term for a land surface that is parallel to the dip of the underlying rock layers. The problem states the strike is N-S and the ground surface slopes 15° to the East. Because it is a dip slope, the bedding must also dip 15° to the East. Therefore, the correct measurement is Strike N-S, Dip 15° E.

Question 4

A professor is explaining strike and dip to an introductory geology class using a topographic map as an analogy for a dipping rock layer. Which feature on the topographic map is most analogous to a strike line?

A line drawn directly down the steepest part of a hill.
A single, continuous contour line. (correct answer)
The blue line representing a stream in a valley.
The north arrow indicating the map's orientation.

Explanation: A strike line on a geologic plane is a line connecting points of equal elevation. A contour line on a topographic map is a line connecting points of equal elevation on the Earth's surface. This makes a contour line the best analogy for a strike line. A line down the steepest part of a hill is analogous to the dip direction.

Question 5

A geologist measures the apparent dip of a single, planar sandstone bed at two different, perpendicular road cuts. On a North-South oriented road cut, the bed appears to dip 20° to the South. On an East-West oriented road cut, the bed appears to dip 35° to the East. What is the most likely true orientation of the sandstone bed?

Strike N-S, Dip 20° S
Strike E-W, Dip 35° E
Strike NW-SE, Dip approximately 40° NE
Strike NE-SW, Dip approximately 40° SE (correct answer)

Explanation: This is a two-apparent-dip problem to find the true strike and dip. When a bed shows apparent dip to the south on one face and to the east on another perpendicular face, the true dip direction must be between these directions (southeast). The true dip magnitude can be calculated using: tan(true dip) = √[tan²(20°) + tan²(35°)] = √[0.364² + 0.700²] = √[0.133 + 0.490] = √0.623 ≈ 0.789. Therefore, true dip ≈ arctan(0.789) ≈ 38-40°. The strike is perpendicular to the dip direction, so a dip to the SE corresponds to a strike of NE-SW.

Question 6

A geologist pours a small amount of water onto a large, smooth, tilted slab of sandstone exposed at the surface. The water is observed to pool and then flow most rapidly along a compass bearing of 135° (SE). What can be most directly inferred from this observation?

The strike of the sandstone slab is approximately 135°.
The dip direction of the sandstone slab is approximately 135°. (correct answer)
The bedding plane of the sandstone is nearly horizontal.
The strike of the sandstone slab is perpendicular to a bearing of 135°.

Explanation: Water flows down the steepest gradient on a surface. For a tilted planar feature like a bedding plane, the direction of steepest descent is the true dip direction. Therefore, the observation that water flows most rapidly towards 135° directly indicates the dip direction. Strike is perpendicular to the dip direction, so it would be N45°E (045°), not 135°. If the plane were horizontal, the water would pool without flowing in a specific direction.

Question 7

Exactly 30°
Exactly 0° (horizontal) (correct answer)
Greater than 30°
Less than 30° but greater than 0°

Question 8

A geologist identifies a tilted sedimentary bed. To determine its strike, she finds a line on the bed's surface along which all points have the exact same elevation. What does the compass direction of this line represent?

The dip direction of the bed.
The strike of the bed. (correct answer)
The axis of the regional fold.
An apparent dip direction.

Explanation: By definition, the strike of a tilted plane is the compass direction (bearing) of a horizontal line on that plane. A line where all points have the same elevation is a horizontal line. Therefore, the compass direction of this line is the strike.

Question 9

A line drawn directly down the steepest part of a hill.
A single, continuous contour line. (correct answer)
The blue line representing a stream in a valley.
The north arrow indicating the map's orientation.

Question 10

A geologic map uses the right-hand rule convention for recording strike and dip. An orientation on this map is recorded as 210/25. What is the compass direction (azimuth) of the dip?

120°
210°
300° (correct answer)
030°

Explanation: The right-hand rule convention states that the strike azimuth is recorded such that the beds dip to the right. To find the dip direction, one adds 90° to the strike azimuth. In this case, the strike is 210°. The dip direction is 210° + 90° = 300°.

Question 11

When measuring the dip angle of a tilted bedding plane, a geologist must orient their clinometer so it measures the inclination of a line drawn perpendicular to the strike. Why is this specific orientation essential for a standard dip measurement?

To ensure the compass reading is not affected by magnetic minerals in the rock.
To measure the maximum possible angle of inclination for that plane. (correct answer)
To find an apparent dip, which is a more stable measurement than true dip.
To align the clinometer parallel to Earth's magnetic field for calibration.

Explanation: The dip of a plane is defined as the maximum angle of inclination measured from horizontal. This maximum angle occurs only along the path of steepest descent, which is a line perpendicular to the strike (a line of no inclination). Measuring along any other direction on the plane will yield a smaller, or apparent, dip angle.

Question 12

Field observations indicate that a sequence of shale beds is dipping at 50° directly towards a compass bearing of 270° (due West). What is the strike of these shale beds?

North-South (000° or 180°) (correct answer)
East-West (090° or 270°)
Northeast-Southwest (045° or 225°)
Northwest-Southeast (315° or 135°)

Explanation: The strike of a planar feature is always perpendicular (90°) to its dip direction. The dip direction is given as due West (270°). The two directions that are 90° from 270° are North (270° + 90° = 360°, or 000°) and South (270° - 90° = 180°). Therefore, the strike is North-South.

Question 13

On a geologic map, the mapped contact between a sandstone and a shale layer is observed to be a perfectly straight line oriented N30°E for several kilometers, despite crossing hills and valleys of varying elevation. What can be concluded about the orientation of this contact plane?

It is a horizontal plane with an elevation of 30 meters.
It is a horizontal plane whose orientation cannot be determined.
It dips at a shallow angle of 30° to the southeast.
It is a vertical plane with a strike of N30°E. (correct answer)

Explanation: When interpreting geologic maps, the key relationship to understand is how rock layer contacts appear on the surface based on their subsurface orientation. The shape and pattern of mapped contacts reveal crucial information about the three-dimensional geometry of rock layers. A perfectly straight contact line that maintains the same orientation (N30°E) across varying topography—hills and valleys of different elevations—indicates that the contact plane must be vertical. Here's why: if a rock layer boundary has any dip (angle from horizontal), it will appear as a curved or zigzagging line on a topographic map because it intersects the ground surface at different elevations. Only vertical planes maintain straight-line contacts regardless of topographic relief, since they cut through the landscape at the same angle everywhere. Looking at the wrong answers: Choice A incorrectly assigns a specific elevation of 30 meters, but the "30°" in the strike direction (N30°E) has nothing to do with elevation—it's a compass bearing. Choice B suggests the plane is horizontal, but horizontal contacts would curve significantly when crossing hills and valleys, following elevation contours. Choice C misinterprets the N30°E bearing as a 30° dip angle and incorrectly determines dip direction—if this were true, the contact would appear curved on the map, not straight. The straight-line contact with strike N30°E confirms answer D: a vertical plane. Study tip: Remember that straight contacts across varied topography always indicate vertical rock layers, while dipping layers create curved contact patterns that follow the landscape's elevation changes.

Question 14

A geologist is trying to measure the strike and dip of a sequence of sedimentary layers that are perfectly horizontal. Which entry would be the most accurate and complete for her field notes?

Strike N-S, Dip 90°
Strike E-W, Dip 0°
Strike is indeterminate, Dip is 0° (correct answer)
Strike is N-S, Dip is indeterminate

Explanation: For a perfectly horizontal plane, the angle of inclination (dip) is 0°. Strike is defined as the direction of a horizontal line on a tilted plane. Since the entire plane is horizontal, a horizontal line can be drawn in any direction. Thus, there is no unique strike direction, and it is considered indeterminate or undefined. Choice C is the only one that correctly identifies both components.

Question 15

A geologist is standing on a single, continuous, planar fault surface. She measures the strike as 030°. She then moves 100 meters in the direction of 300° and finds that her elevation on the fault surface has decreased. What does this observation imply about the dip of the fault?

The fault dips towards 120°.
The fault dips towards 210°.
The fault is a strike-slip fault with no dip.
The fault dips towards 300°. (correct answer)

Explanation: This question tests your understanding of how strike and dip relate to the three-dimensional orientation of fault surfaces. When analyzing fault geometry, you need to visualize how movement across the fault surface affects elevation changes. The key insight is that if you move perpendicular to the strike direction and experience an elevation change, you're moving in the dip direction. Since the strike is 030°, the two possible dip directions are perpendicular to this: either 120° (030° + 90°) or 300° (030° - 90°). The geologist moved toward 300° and went downhill on the fault surface, meaning the fault surface slopes downward in that direction. Therefore, the fault dips toward 300°, making D correct. A is wrong because 120° is the opposite dip direction. If the fault dipped toward 120°, moving toward 300° would take you uphill on the fault surface, not downhill as observed. B is incorrect because 210° is parallel to the strike direction (030° + 180°), not perpendicular to it. Moving parallel to strike doesn't change elevation on a dipping surface. C misinterprets the observation entirely—the elevation change proves the fault does have dip. Strike-slip faults can still have dip; the term refers to the direction of movement, not the fault's orientation. Remember this relationship: when you move perpendicular to strike and go downhill, you're moving in the dip direction. Always check that your dip direction is 90° from the strike direction, and use elevation changes to determine which of the two perpendicular directions is correct.

Question 16

The dip direction of the bed.
The strike of the bed. (correct answer)
The axis of the regional fold.
An apparent dip direction.

Question 17

Strike N-S, Dip 20° S
Strike E-W, Dip 35° E
Strike NW-SE, Dip approximately 40° NE
Strike NE-SW, Dip approximately 40° SE (correct answer)

Question 18

The trace of a dipping rock layer forms a 'V' shape where it crosses a river valley on a map. The 'V' is observed to point in the upstream direction. What can be concluded about the dip of the rock layer?

The layer is horizontal.
The layer is dipping in the upstream direction.
The layer is dipping in the downstream direction. (correct answer)
The layer is vertical.

Explanation: This question refers to the 'Rule of V's'. When a dipping layer crosses a valley, the map trace of the layer forms a 'V'. If the layer dips in the downstream direction (at an angle steeper than the valley gradient), the 'V' points upstream. If the layer dips upstream, the 'V' points downstream. If the layer is horizontal, its trace follows contour lines. If it is vertical, its trace is a straight line.

Question 19

To ensure the compass reading is not affected by magnetic minerals in the rock.
To measure the maximum possible angle of inclination for that plane. (correct answer)
To find an apparent dip, which is a more stable measurement than true dip.
To align the clinometer parallel to Earth's magnetic field for calibration.

Question 20

Strike N-S, Dip 15° W
Strike E-W, Dip 15° E
Strike N-S, Dip 15° E (correct answer)
Strike N-S, Dip cannot be determined from this information.