I think I saw a nice map like this a while back on the forums. It had a river and a MASSIVE canyon dividing the map in two, with a really tall but small waterfall.
I don't have the map, but if you give me two secs I'll post the world-gen parameters.
EDIT:
[WORLD_GEN]
[TITLE:WATERFALL]
[SEED:3512849536]
[HISTORY_SEED:667583488]
[NAME_SEED:1355469248]
[DIM:257:257]
[END_YEAR:400]
[BEAST_END_YEAR:400:80]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:1]
[ELEVATION:1:400:1600:1600]
[RAINFALL:0:100:400:400]
[TEMPERATURE:25:75:400:400]
[DRAINAGE:0:100:400:400]
[VOLCANISM:5:100:400:400]
[SAVAGERY:50:100:100:100]
[ELEVATION_FREQUENCY:1:1:1:1:1:1]
[RAIN_FREQUENCY:1:1:1:1:1:1]
[DRAINAGE_FREQUENCY:1:1:1:1:1:1]
[TEMPERATURE_FREQUENCY:1:1:1:1:1:1]
[SAVAGERY_FREQUENCY:1:1:1:1:1:1]
[VOLCANISM_FREQUENCY:1:1:1:1:1:1]
[GOOD_SQ_COUNTS:50:500:700]
[EVIL_SQ_COUNTS:100:1000:2000]
[PEAK_NUMBER_MIN:0]
[OCEAN_EDGE_MIN:1]
[VOLCANO_MIN:15]
[REGION_COUNTS:SWAMP:1032:7:6]
[REGION_COUNTS:DESERT:1032:7:6]
[REGION_COUNTS:FOREST:4128:13:12]
[REGION_COUNTS:MOUNTAINS:8256:9:9]
[REGION_COUNTS:OCEAN:0:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:8256:13:12]
[REGION_COUNTS:HILLS:8256:13:12]
[EROSION_CYCLE_COUNT:0]
[RIVER_MINS:400:400]
[PERIODICALLY_ERODE_EXTREMES:0]
[OROGRAPHIC_PRECIPITATION:1]
[SUBREGION_MAX:2750]
[CAVE_MIN_SIZE:5]
[CAVE_MAX_SIZE:25]
[MOUNTAIN_CAVE_MIN:100]
[NON_MOUNTAIN_CAVE_MIN:200]
[ALL_CAVES_VISIBLE:1]
[SHOW_EMBARK_RIVER:2]
[SHOW_EMBARK_POOL:2]
[SHOW_EMBARK_M_POOL:2]
[SHOW_EMBARK_M_PIPE:2]
[SHOW_EMBARK_CHASM:2]
[SHOW_EMBARK_PIT:2]
[SHOW_EMBARK_OTHER:2]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:50]
[TOTAL_CIV_POPULATION:20000]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:8256:16512:8256]
[RAIN_RANGES:8256:16512:8256]
[DRAINAGE_RANGES:8256:16512:8256]
[SAVAGERY_RANGES:0:0:8256]
[VOLCANISM_RANGES:8256:16512:8256]
Here you go. I'm not quite sure where in the world it is, but it's on a major river.
EDIT2:
http://www.bay12games.com/forum/index.php?topic=38264.0 Here's the thread I dragged it from.