Dinah Hall is on holiday

Iowa is one of those places that makes people laugh even if they haven't been there. I can understand this. I mean I was born there and have always felt immensely grateful that my parents decided to move around the same time as the doctor cut the umbilical cord. Still it does seem strange that people in England who probably do not even know that Iowa is a state in the American Midwest find it so funny when I say I am planning a visit. "Why?" they hoot and try to change the subject.

I refuse to do this. The latest therapy word to invade the American language is "closure" and I know that my Iowa conversation is nowhere near that point yet. "To see my grandmother," I say. This stops the conversation dead and there is a moment in which everyone lowers their eyes. I think they are waiting for me to admit that I am lying, that I have invented this grandmother in a sad attempt to shave a few years off my age. I'm sure they are thinking: "Why can't she just have a little eyebag surgery like everyone else?"

In fact, my grandmother's existence sometimes does seem a little unreal even to me. Part of this is that there has always been at least 1,000 miles between us and also that Iowa itself can seem pretty unreal (even if you were born there). For instance, the entire state is laid out on a grid plan and so it is not unusual to come across, say, 159th street in the middle of nowhere. I was last in Iowa five years ago for my grandmother's 90th birthday and drove straight (and I do mean straight) across the state, listening to the radio. The big news item of the day was a kerbside lawnmower theft. "If you know anything about this, please do contact the police," the announcer emphasised before breaking off for that day's recipe.

This time I drove north, following the Mississippi River, through a green Grant Wood landscape, and tried to imagine what the place looked like in my grandmother's mind. She is now 95 and was born and raised, courted and married here. She lived through the Depression and two world wars and had four children, 12 grandchildren and even more great-grandchildren. It's been a good life and I suspect (though she would never say) that she has been waiting to die for some time.

Seeing her was a shock, not because she has changed but because the older she gets the younger I feel. She is tiny, ultra-feminine and sharp as a tack. Next to her I am suddenly a hulking teenager. I certainly am not a single mother of two who is in charge of everything from packed lunches to negative equity. "Drink your milk up!" my grandmother exclaims over lunch and for a moment I feel exactly like my teenage daughter must when I say the same thing to her.

Isn't it strange how little we know about our own families? I spend my life interviewing other people and yet I know only snippets of my own grandmother's long life. Now I know a bit more because she has written up some of her memories. They start, as she did, in 1902. "My father was a farmer, he loved the prairie. His favourite flower was the goldenrod. My mother was a dressmaker and a musician." Her childhood was another world: a place of barefoot summers and of catching frogs, a time when you got one present at Christmas and grandparents came to visit in a one- horse shay and used a buffalo robe to keep out the cold.

When she was five she and her sister were walking the one mile home from school one day when the strangest contraption came down the road. "We ran into the cornfield, hid ourselves and watched, in awe. This was the first time I saw an auto." There was a family cow, hundreds of chickens and a barrel of butchered hog on the back porch for the long winter. "When mother wanted some meat, she would have to take a pick, pry the meat loose, thaw it out." She writes of hitching up the horse to go to her high school graduation in the middle of a scarlet fever outbreak and of the curfews and fruit punch parties of teaching college. At 19 she took her first job in a one-room country schoolhouse. So far the memoirs stop at 1924 and I can only hope for more.

I look over at her as we drive to dinner. Could she get any lighter? In comparison, the car door seems impossibly heavy. She is unsteady on her feet and perhaps one day she will just float away. I am thinking these thoughts as we sit in a car park, waiting for another car to move. "Oh, honk your horn. Honk! This is ridiculous," she fumes. Road rage in deepest Iowa seems a little unreal, but then again, so does being a granddaughter. Thank god that car moved and I didn't have to honk.