Do other countries have ‘gullies’? – I am not sure. The dictionary tells me they are also known as ‘small valleys’ and ‘ravines’. ‘Valley’, even of the diminutive kind, seems a bit too bucoIic to me, while ‘ravine’ sounds way too treacherous (though in fairness, some gullies are pretty precipitous).
In New Zealand, and especially the North Island where we live, the country is dissected by gullies running from the foothills of mountains and mountain chains, created by water running from these watersheds. Sometimes the streams that have created them are ephemeral – they dry up completely over the summer months. And often the gully dwarfs the skinny little waterway that runs down the bottom – hinting at more water-abundant times, perhaps after a previous ice age, when icesheets melted away, disgorging their contents as trickles that eventually became rock-gouging torrents.
Gullies, by their damp and recessed nature, often escaped the worst ravages of the European settlers’ forest clearance through fire and milling. Even if damaged, their unworkable terrain means they are more likely to have restored some of their tree cover, becoming oases of indigenous nature in an otherwise homogenous pastoral landscape. Even so, many gullies became convenient dumping grounds for farmers and householders alike, of old farming equipment, sheep and cattle carcasses, tyres, and general household rubbish. But many landowners today have come to value and protect gullies as important vestiges of indigenous nature and ecosystems of the lowlands and hill country.
Of course, the key challenge a gully presents to anyone lucky enough to have access to one, is how to get down it, with only a small chance of permanently maiming yourself. This becomes particularly important if you have youngsters. In our case, a series of footholds dug with a spade, ropes knotted at intervals, and a 2 1/2-metre high ladder did the trick. 
And what an exciting world it has opened up for us. A discovery around every bend, on every fern and moss-covered gully-face, in every gully wall cavity. We now know where the kingfishers nest (in cliff-face burrows) and the kereru brings up her babies (high in a rewarewa tree). This is an entirely different ecosystem from the one we know up above – it is damp, cool, dark and largely windless – even on the windiest day. It is one that rewards the tenacious (trees that can grow sideways) and the moisture-loving.
It also makes you think very differently about how Aotearoa’s first explorers traveled the country. Where dense forest made travel difficult (i.e., pretty much everywhere), these little gullies, with stoney streambeds largely free of vegetation, would have offerred a convenient means of traversing terrain.
In this sense then, these gullies, which converge and diverge in a vast network, similar to veins in a body or an (admittedly haphazard) roading system, are ‘subterranean’ – a secret world, for those of us lucky enough to explore them.
envirohistory NZ 
Gullies are plentiful and loved on the south side of Lyttelton Harbour! There’s a community planting day in Morgans Gully, Diamond Harbour on October 28 (https://diamondharbour.info/venue/morgans-gully/) and other local gullies (Sam’s Guily and Hunter’s gully) have also had planting and weed control done by the community. These gullies run off the slopes of Mt Herbert to the Harbour. Some are quite shallow, and some are steep and challenging (e.g. Magnificent Gully at Orton Bradley Park). All have small creeks in them, which dry up in hot summers.
I agree with you that scrambling up a gully is great fun at any age.
That’s great Christine – sounds like gullies are getting a lot of love in your neck of the woods.
In the Dominican Republic, such gullies are called “caniadas” (that ni is my anglicized n-tilde). We are fortunate to have two of them – though not so magnificently deep as yours appear to be. Still, they are distinctive – notably more moist than the surrounding forest. I guess any mountainous area has them, but the name varies quite a bit. Back home in Virginia, they were not so deep (very old mountains), so hardly distinctive. Backpacking and following topographic contours we just called them valleys despite that we knew the “real” valley was down below – between the mountain ridges. We would only have called them a gulley if they were eroded deeply with banks not passable by simple walking.
Thank you so much Cade for these interesting insights from the Dominican Republic and Virginia – nice to know that gullies (or however they are known) are valued in other parts of the world too.