This is one of those lists where you bold the things you've seen or done. I was surprised at how well I did (26 and a couple halves) considering I'm not a geologist and not especially well traveled. Fortunately, the northwest corner of North America is a very geologically rich territory. I could have done even better. When I was a kid, my family traveled through a few more places on the list and either didn't stop or had no idea what we were seeing. Chris Rowan, the main geology blogger over at ScienceBlogs got 38 and a couple halves.
1. See an erupting volcano. [I've seen Mts. Illiamna and Spurr in Alaska spew ash and smoke]
2. See a glacier. I've stomped around on several in Alaska and British Columbia]
3. See an active geyser See an active geyser such as those in Yellowstone, New Zealand or the type locality of Iceland. [Yellowstone several times as a kid]
4. Visit the Cretaceous/Tertiary (KT) Boundary.
5. Observe (from a safe distance) a river whose discharge is above bankful stage.
6. Explore a limestone cave. [Lewis and Clark Caverns in Montana]
7. Tour an open pit mine. [I visited the Berkeley Pit in Butte, Montana when it was still operating]
8. Explore a subsurface mine. [I've never been deep inside one, but I have nosed around the opening to some abandoned mines in Alaska, Idaho, and Montana]
9. See an ophiolite, such as the ophiolite complex in Oman or the Troodos complex on the Island Cyprus.
10. An anorthosite complex, such as those in Labrador, the Adirondacks, and Niger (there's some anorthosite in southern California too).
11. A slot canyon. Many of these amazing canyons are less than 3 feet wide and over 100 feet deep. [Tokkum Creek in Kootenay National Park, British Columbia]
12. Varves, whether you see the type section in Sweden or examples elsewhere.
13. An exfoliation dome, such as those in the Sierra Nevada.
14. A layered igneous intrusion, such as the Stillwater complex in Montana or the Skaergaard Complex in Eastern Greenland. [not sure if this counts. I went camping in the Stillwater as a kid, without knowing what it was]
15. Coastlines along the leading and trailing edge of a tectonic plate. [Only one side, so far]
16. A gingko tree, which is the lone survivor of an ancient group of softwoods that covered much of the Northern Hemisphere in the Mesozoic.
17. Living and fossilized stromatolites (Glacier National Park is a great place to see fossil stromatolites, while Shark Bay in Australia is the place to see living ones)
18. A field of glacial erratics. [Alaska, of course]
19. A caldera. [Yellowstone again]
20. A sand dune more than 200 feet high.
21. A fjord. [Southeastern Alaska and British Columbia]
22. A recently formed fault scarp. [we moved to Alaska a few years after the Good Friday earthquake of 1964 and there were two good fault scarps still visible in Anchorage]
23. A megabreccia.
24. An actively accreting river delta. [not a big one, but lots of little ones on Alaska]
25. A natural bridge.
26. A large sinkhole.
27. A glacial outwash plain [Alaska and Canadian Rockies.]
28. A sea stack. [Oregon and Washngton coasts]
29. A house-sized glacial erratic. [the biggest I've seen was about the sise of an old Buick]
30. An underground lake or river.
31. The continental divide. [many, many times]
32. Fluorescent and phosphorescent minerals.
33. Petrified trees. [no whole sections of trees, but I have some chunks of petrified wood that I collected as a kid]
34. Lava tubes. [in a couple places in sotheastern Idaho].
35. The Grand Canyon. All the way down. And back.
36. Meteor Crater, Arizona, also known as the Barringer Crater, to see an impact crater on a scale that is comprehensible.
37. The Great Barrier Reef, northeastern Australia, to see the largest coral reef in the world.
38. The Bay of Fundy, New Brunswick and Nova Scotia, Canada, to see the highest tides in the world (up to 16m). [Cook Inlet Alaska has the second highest tides, up to about 14m]
39. The Waterpocket Fold, Utah, to see well exposed folds on a massive scale.
40. The Banded Iron Formation, Michigan, to better appreciate the air you breathe.
41. The Snows of Kilimanjaro, Tanzania,
42. Lake Baikal, Siberia, to see the deepest lake in the world (1,620 m) with 20 percent of the Earth's fresh water.
43. Ayers Rock (known now by the Aboriginal name of Uluru), Australia. This inselberg of nearly vertical Precambrian strata is about 2.5 kilometers long and more than 350 meters high.
44. Devil's Tower, northeastern Wyoming, to see a classic example of columnar jointing.
45. The Alps. [I flew over them, they look a lot like the Canadian Rockies, but smaller]
46. Telescope Peak, in Death Valley National Park. From this spectacular summit you can look down onto the floor of Death Valley - 11,330 feet below.
47. The Li River, China, to see the fantastic tower karst that appears in much Chinese art.
48. The Dalmatian Coast of Croatia, to see the original Karst.
49. The Gorge of Bhagirathi, one of the sacred headwaters of the Ganges, in the Indian Himalayas, where the river flows from an ice tunnel beneath the Gangatori Glacier into a deep gorge.
50. The Goosenecks of the San Juan River, Utah, an impressive series of entrenched meanders.
51. Shiprock, New Mexico, to see a large volcanic neck.
52. Land's End, Cornwall, Great Britain, for fractured granites that have feldspar crystals bigger than your fist.
53. Tierra del Fuego, Chile and Argentina, to see the Straights of Magellan and the southernmost tip of South America.
54. Mount St. Helens, Washington, to see the results of recent explosive volcanism.
55. The Giant's Causeway and the Antrim Plateau, Northern Ireland, to see polygonally fractured basaltic flows.
56. The Great Rift Valley in Africa.
57. The Matterhorn, along the Swiss/Italian border, to see the classic "horn".
58. The Carolina Bays, along the Carolinian and Georgian coastal plain
59. The Mima Mounds near Olympia, Washington
60. Siccar Point, Berwickshire, Scotland, where James Hutton (the "father" of modern geology) observed the classic unconformity.
61. The moving rocks of Racetrack Playa in Death Valley
62. Yosemite Valley
63. Landscape Arch (or Delicate Arch) in Utah
64. The Burgess Shale in British Columbia. [This is one we drove past, when I was a kid, without knowing what was there]
65. The Channeled Scablands of central Washington
66. Bryce Canyon
67. Grand Prismatic Spring at Yellowstone
68. Monument Valley
69. The San Andreas fault
70. The dinosaur footprints in La Rioja, Spain
71. The volcanic landscapes of the Canary Islands
72. The Pyrenees Mountains
73. The Lime Caves at Karamea on the West Coast of New Zealand
74. Denali (an orogeny in progress)
75. A catastrophic mass wasting event.
76. The giant crossbeds visible at Zion National Park .
77. The black sand beaches in Hawaii (or the green sand-olivine beaches).
78. Barton Springs in Texas.
79. Hells Canyon in Idaho
80. The Black Canyon of the Gunnison in Colorado.
81. The Tunguska Impact site in Siberia.
82. Feel an earthquake with a magnitude greater than 5.0. [several in Alaska and one in Seattle]
83. Find dinosaur footprints in situ.
84. Find a trilobite (or a dinosaur bone or any other fossil).
85. Find gold, however small the flake. [gold panning was one my regular summer pastimes as a kid]
86. Find a meteorite fragment
87. Experience a volcanic ashfall.[Mts. St Augustine and Spurr in Anchorage]
88. Experience a sandstorm.
89. See a tsunami.
90. Witness a total solar eclipse. [only partials]
91. Witness a tornado firsthand (Important rules of this game).
92. Witness a meteor storm, a term used to describe a particularly intense (1000+ per minute) meteor shower
93. View Saturn and its moons through a respectable telescope.
94. See the Aurora borealis, otherwise known as the northern lights. [many times]
95. View a great naked-eye comet, an opportunity which occurs only a few times per century. [Hyahkutake in 1996]
96. See a lunar eclipse. [both full and partial]
97. View a distant galaxy through a large telescope
98. Experience a hurricane.
99. See noctilucent clouds. [maybe]
100. See the green flash.
If they're going list atmospheric phenomena, I think I should get credit for sundogs and solar halos.