Write an install image to a flash drive?

[Bob Bernstein <poobah%ruptured-duck.com@localhost>]

I want to use a flash drive instead of a CD to upgrade from an 
old 'current' to our latest. This is being done on an ancient 
emachine amd64:

NetBSD nebby 8.99.35 NetBSD 8.99.35 (GENERIC) #0: Wed Mar 13 06:27:34 UTC 2019  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64

I am new to flash drives. I did the following with a new 
Kingston 64GB right out of its FedEx mailing envelope:

dd if=boot.iso of=/dev/rsd1d bs=1m

The boot.iso was: 
http://nycdn.netbsd.org/pub/NetBSD-daily/HEAD/latest/amd64/installation/cdrom/boot.iso 

Rebooting the emachine, it gave me a choice to boot from the 
Kingston, but there was no joy in Mudville. All attempts reverted 
to booting normally from the hd.

Trying 'mount /dev/sd1' /mnt yielded "bad superblock." (Pretty 
sure; I am typing these results from memory.)

I _can't imagine_ how many stupid things I just did, but could 
someone please tell me how to get that install image onto the 
flash drive in a form that will boot?

Thank you
 

-- 
What can be asserted without evidence can be 
dismissed without evidence.
                             Hitchens' Razor