It would depend on how broadly you define geography. So, for example, the State of Illinois in the United States runs more than 300 miles from it's northern border to Cairo, Illinois, near where the Ohio River runs into the Mississippi River. Most of Illinois is a geological region which is called glacial till plain. That means that the ice sheet of the last ice age scraped it into a relatively flat plain. The southern extremity of the state, however, is in a geological region known as the Shawnee Hills. The environment there is readically different from the farmland in northern Illinois.
Define your georgraphy more narrowly, and one can still find radical differences. The city of Toronto, Ontariio, in Canada, stretches along the northern shore of Lake Ontario. Temperatures there are usually a few to several degrees cooler than those on the bluffs above the lake where most of the city lies. Leaving aside the fact of an urban environment, the conditions which prevail on the bluffs are quite different than those on the lake shore. There is a river that runs through Toronto, the Don River, and it cuts down through the bluff (at the highest point, the bluffs are 300 feet above the lake). The environment there, at the river banks, is quite different from the environment on top of the bluffs. There is an abandoned clay quarry in the Don valley known as the Brick Works (there was once a brick works operating there). Ten years ago, there was a beaver lodge in the low point of the quarry. (The Brick Works has now become a stylish, trendy area, with office space and weekend markets--the beavers have long since abandoned the area.)
You can narrow it down even further. At the deepest point, the Grand Canyon is more than 6000 feet deep. It runs for quite a distance, but you could look at just a mile of its length and find a great deal of diversity. This is from the National Park Service web site:
The Park contains several major ecosystems. Its great biological diversity can be attributed to the presence of five of the seven life zones and three of the four desert types in North America. The five life zones represented are the Lower Sonoran, Upper Sonoran, Transition, Canadian, and Hudsonian. This is equivalent to traveling from Mexico to Canada. The Park also serves as an ecological refuge, with relatively undisturbed remnants of dwindling ecosystems (such as boreal forest and desert riparian communities). It is home to numerous rare, endemic (found only at Grand Canyon), and specially protected (threatened or endangered) plant and animal species.
Over 1,500 plant, 355 bird, 89 mammalian, 47 reptile, 9 amphibian, and 17 fish species are found in park.
How you define geography determines the answer to your question. But the examples of the Scarborough Bluffs in Toronto, and the Grand Canyon show that there can be a great deal of diversity in a relatively small space. Keep in mind that geography is an artificial, human construct which is overlaid on reality.