The worldgen parameter set below produces at least 10 river canyons of a depth of 50Z levels, per world, with varying widths of rivers.
It's entirely artificial, in the sense that the elevations are manually placed with the painter in advanced worldgen. However, it should get you on the right path to trying to generate what you want, Arkhon Skyhex.
It should be noted, though, that what you're trying to do is trivially accomplished in DFHack, even if you wanted to create the entire thing from scratch on an entirely random embark. Getting actual natural SHEER cliffs, that is, cliffs that traverse more than 7 Z-levels with no natural ramps, is quite challenging. There's only two "natural" ways to obtain said cliffs that I know of in DF.
The first is via river canyons, hence my post here.
The second is by finding a lake adjacent to a mountain (or other extreme elevation change) and the lake "shore" will be vertical from the non lake biome into the lake, at the edge. Those are rare and unpredictable.
Personally, if I were attempting
such a project, I would find a nice sloping mountain, channel out the water paths and then place river source tiles with DFHack liquids. Often, I find when people say cliffs, they just mean a 1:1 rise:run slope, because they've never actually seen a sheer cliff face in the game. In any case, either is possible, with varying degrees of ease or pain.
[WORLD_GEN]
[TITLE:RIVER_CANYONS]
[DIM:33:33]
[EMBARK_POINTS:5000]
[END_YEAR:100]
[BEAST_END_YEAR:100:-1]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:0]
[ELEVATION:1:400:0:0]
[RAINFALL:100:100:0:0]
[TEMPERATURE:75:75:0:0]
[DRAINAGE:100:100:0:0]
[VOLCANISM:0:0:0:0]
[SAVAGERY:0:0:0:0]
[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]
[POLE:NORTH]
[MINERAL_SCARCITY:1000]
[MEGABEAST_CAP:0]
[SEMIMEGABEAST_CAP:0]
[TITAN_NUMBER:0]
[TITAN_ATTACK_TRIGGER:40:0:0]
[DEMON_NUMBER:2]
[NIGHT_TROLL_NUMBER:0]
[BOGEYMAN_NUMBER:0]
[VAMPIRE_NUMBER:0]
[WEREBEAST_NUMBER:0]
[SECRET_NUMBER:0]
[REGIONAL_INTERACTION_NUMBER:0]
[DISTURBANCE_INTERACTION_NUMBER:0]
[EVIL_CLOUD_NUMBER:0]
[EVIL_RAIN_NUMBER:0]
[GENERATE_DIVINE_MATERIALS:0]
[GOOD_SQ_COUNTS:0:0:0]
[EVIL_SQ_COUNTS:0:0:0]
[PEAK_NUMBER_MIN:0]
[PARTIAL_OCEAN_EDGE_MIN:0]
[COMPLETE_OCEAN_EDGE_MIN:0]
[VOLCANO_MIN:0]
[REGION_COUNTS:SWAMP:0:0:0]
[REGION_COUNTS:DESERT:0:0:0]
[REGION_COUNTS:FOREST:0:0:0]
[REGION_COUNTS:MOUNTAINS:0:0:0]
[REGION_COUNTS:OCEAN:0:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:0:0:0]
[REGION_COUNTS:HILLS:0:0:0]
[EROSION_CYCLE_COUNT:999]
[RIVER_MINS:0:0]
[PERIODICALLY_ERODE_EXTREMES:0]
[OROGRAPHIC_PRECIPITATION:0]
[SUBREGION_MAX:2700]
[CAVERN_LAYER_COUNT:1]
[CAVERN_LAYER_OPENNESS_MIN:5]
[CAVERN_LAYER_OPENNESS_MAX:0]
[CAVERN_LAYER_PASSAGE_DENSITY_MIN:0]
[CAVERN_LAYER_PASSAGE_DENSITY_MAX:0]
[CAVERN_LAYER_WATER_MIN:51]
[CAVERN_LAYER_WATER_MAX:60]
[HAVE_BOTTOM_LAYER_1:1]
[HAVE_BOTTOM_LAYER_2:1]
[LEVELS_ABOVE_GROUND:10]
[LEVELS_ABOVE_LAYER_1:8]
[LEVELS_ABOVE_LAYER_2:20]
[LEVELS_ABOVE_LAYER_3:2]
[LEVELS_ABOVE_LAYER_4:2]
[LEVELS_ABOVE_LAYER_5:3]
[LEVELS_AT_BOTTOM:2]
[CAVE_MIN_SIZE:1]
[CAVE_MAX_SIZE:1]
[MOUNTAIN_CAVE_MIN:0]
[NON_MOUNTAIN_CAVE_MIN:0]
[ALL_CAVES_VISIBLE:1]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:3]
[TOTAL_CIV_POPULATION:2]
[SITE_CAP:20]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:0:0:0]
[RAIN_RANGES:0:0:0]
[DRAINAGE_RANGES:0:0:0]
[SAVAGERY_RANGES:0:0:0]
[VOLCANISM_RANGES:0:0:0]
[PS_EL:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400]
[PS_EL:400:400:400:400:400:400:400:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:400:400:400:400:400:400:400]
[PS_EL:400:400:400:400:400:400:400:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:400:400:400:400:400:400:400]
[PS_EL:400:200:100:148:146:144:142:140:138:136:134:132:130:128:126:124:122:120:118:116:114:112:110:108:106:104:102:100:100:100:400:400:400]
[PS_EL:400:400:400:400:400:400:400:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:400:400:400:100:400:400:400]
[PS_EL:400:400:400:400:400:400:400:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:400:400:299:100:299:400:400]
[PS_EL:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:100:400:400:400]
[PS_EL:400:400:400:400:400:400:400:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:400:400:299:100:299:400:400]
[PS_EL:400:400:400:400:400:400:400:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:400:400:400:100:400:400:400]
[PS_EL:400:400:400:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:400:400:400]
[PS_EL:400:400:400:100:400:400:400:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:400:400:400:400:400:400:400]
[PS_EL:400:400:299:100:299:400:400:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:400:400:400:400:400:400:400]
[PS_EL:400:400:400:100:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400]
[PS_EL:400:400:299:100:299:400:400:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:400:400:400:400:400:400:400]
[PS_EL:400:400:400:100:400:400:400:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:400:400:400:400:400:400:400]
[PS_EL:400:400:400:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:400:400:400]
[PS_EL:400:400:400:400:400:400:400:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:400:400:400:100:400:400:400]
[PS_EL:400:400:400:400:400:400:400:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:400:400:299:100:299:400:400]
[PS_EL:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:100:400:400:400]
[PS_EL:400:400:400:400:400:400:400:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:400:400:299:100:299:400:400]
[PS_EL:400:400:400:400:400:400:400:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:400:400:400:100:400:400:400]
[PS_EL:400:400:400:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:400:400:400]
[PS_EL:400:400:400:100:400:400:400:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:400:400:400:400:400:400:400]
[PS_EL:400:400:299:100:299:400:400:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:400:400:400:400:400:400:400]
[PS_EL:400:400:400:100:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400]
[PS_EL:400:400:299:100:299:400:400:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:400:400:400:400:400:400:400]
[PS_EL:400:400:400:100:400:400:400:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:400:400:400:400:400:400:400]
[PS_EL:400:400:400:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:400:400:400]
[PS_EL:400:400:400:400:400:400:400:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:400:400:400:100:400:400:400]
[PS_EL:400:400:400:400:400:400:400:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:200:400:400:299:100:299:400:400]
[PS_EL:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:100:400:400:400]
[PS_EL:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:299:100:299:400:400]
[PS_EL:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:400:100:400:400:400]