Pinched this from all over what seems to be called "The GeoBlogoSphere". It does seem a bit biased towards North America, but not to worry. I've only being doing this a few years, so I expect I'll get a pretty minimal score, but it's nice to see what is out there to be seen in the future.
Bold the ones that you've done:
1. See an erupting volcano
2. See a glacier
3. See an active geyser
(Yellowstone, New Zealand or the type locality of Iceland)
4. Visit the Cretaceous/Tertiary (KT) Boundary - I saw this on a summer school trip. Newhaven, East Sussex.
(Possible locations include Gubbio, Italy, Stevns Klint, Denmark, the Red Deer River Valley near Drumheller, Alberta.)
5. Observe (from a safe distance) a river whose discharge is above bankful stage
6. Explore a limestone cave - turns out that Wookey Hole is a limestone cave and therefore counts. I've tourned one in Spain as well, but can't recall the name
(Try Carlsbad Caverns in New Mexico, Lehman Caves in Great Basin National Park, or the caves of Kentucky)
7. Tour an open pit mine - I had to Google this to why this was different to quarries. Well, by the looks of things it isn't. So I've done field trips to mines twice.
(Such as those in Butte, Montana, Bingham Canyon, Utah, Summitville, Colorado, Globe or Morenci, Arizona, or Chuquicamata, Chile.)
8. Explore a subsurface mine - they took us to one in Cornwall when I was at school!
9. See an ophiolite, such as the ophiolite complex in Oman or the Troodos complex on the Island Cyprus (if on a budget, try the Coast Ranges or Klamath Mountains of California).
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 - Zion National Park, Utah. Just stumbled across one with nobody around, so I've actually pee'd in slot canyon!
(Many of these amazing canyons are less than 3 feet wide and over 100 feet deep. They reside on the Colorado Plateau. Among the best are Antelope Canyon, Brimstone Canyon, Spooky Gulch and the Round Valley Draw.)
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.
15. Coastlines along the leading and trailing edge of a tectonic plate
16. A gingko tree - ooo! Typo! They mean a Ginkgo biloba, of course...
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 Yep. They took us to see some at Summer School in 2009!
(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
19. A caldera
20. A sand dune more than 200 feet high
21. A fjord
22. A recently formed fault scarp
23. A megabreccia
24. An actively accreting river delta
25. A natural bridge
26. A large sinkhole - not seen a large one
27. A glacial outwash plain
28. A sea stack - The Needles! Then they showed us one at Summer School in '09.
29. A house-sized glacial erratic - how big does the house have to be? I've seen shed-sized...
30. An underground lake or river - the River Axe flows through Wookey Hole, so I'm guessing that this one is a yes
31. The continental divide - just ticked this one off back in October!
32. Fluorescent and phosphorescent minerals - in musuems, not kicking around on the ground! Geology Museum in Barcelona a couple of weeks ago was the most recent.
33. Petrified trees - Petrified Forest, Arizona
34. Lava tubes - they were collapsed, but I'm counting them
35. The Grand Canyon - with all those warnings about how the super-fit can die going down in the canyon? No thank you. I'm counting it because I've been there twice now AND done the North Rim.
(All the way down. And back.)
36. Meteor Crater, Arizona - YAY!!!! I'd wanted to see this for such a long time!!!
(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)
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 (I've seen some of that!)
45. The Alps - something European? Careful there, list-maker.
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 Dalmation 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
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 Pyrennees 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. Love, Love, LOVE!
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.
83. Find dinosaur footprints in situ
84. Find a trilobite (or a dinosaur bone or any other fossil) - many belemnites/ammonites/brachiopods/traces etc
85. Find gold, however small the flake
86. Find a meteorite fragment
87. Experience a volcanic ashfall
88. Experience a sandstorm
89. See a tsunami
90. Witness a total solar eclipse
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.
95. View a great naked-eye comet, an opportunity which occurs only a few times per century
96. See a lunar eclipse
97. View a distant galaxy through a large telescope
98. Experience a hurricane
99. See noctilucent clouds
100. See the green flash
Sadly, a mere 26 things. In fact, I'm pretty lucky that I did that road trip with my Dad in October, as at least 6 items on this list were ticked off then! I'm not sure I want to do some of them, I'll happily continue without being in a hurricane, tornado, sandstorm or be near a tsunami etc. It looks like a tour of The Canyons of America will get most of this list done and dusted!