Treatment for enteric parasites is a common practice in beef cattle, yet little data is known about the prevalence of nematode and trematode parasite infections in beef cattle in the western United States. Likewise, the data on the efficacy of deworming practices and the presence of anthelmintic resistance (AR) of these parasites in this region is sparse. The current study collected evidence for the presence of nematode and trematode parasites in 18 herds of young beef cattle grazing either dryland or irrigated pasture in northern California as well as on efficacy and evidence of AR in a subgroup of herds. We found variable levels of fecal egg counts (FEC) ranging from 6 to 322 for the arithmetic mean eggs per gram (EPG) in the tested cattle groups. There was no difference in the number of EPG between herds grazing dryland or irrigated pasture (P = 0.54). We did not find any evidence for liver flukes or lungworms in the tested cattle. There was evidence of AR to macrocyclic lactones in all eight herds where fecal egg count reduction tests (FECRT) were performed, however due to types and execution of treatment applications and sample sizes, these results need to be interpreted with caution. The most common genus of third stage larvae in coproculture testing before treatment was Cooperia (between 55% and 98% of larvae) as well as post treatment for those herds undergoing FECRT (between 50% and 96%). Ostertagia was the second most frequent genus of larvae found in coproculture testing making up between 0% and 27% of larvae before treatment and between 5% and 50% of larvae after treatment. Anthelmintic practices in beef herds in northern California and likely in a larger geographic area in the western United States need to be updated in order to continue effective use of the currently available drugs. Nematode fecal egg counts are variable in young cattle grazing both irrigated pasture and dryland in northern California. Cooperia and Ostertagia , both common nematode genera shed in young grazing cattle, may show signs of macrocyclic lactone resistance. Beef cattle are routinely treated for intestinal parasites with drugs labeled for this purpose, but little data are available on how common infections with these parasites are in beef cattle in the western United States. There is also sparse data on how much resistance to the available drugs exists in intestinal parasites in this region. The current study collected data on evidence for the presence of roundworm and liver flukes in 18 herds of young beef cattle grazing dryland or irrigated pasture in northern California as well as how effective currently used drugs are in killing them. Mean parasite eggs per gram (EPG) per herd tested in fecal samples ranged from 6 to 322, while no liver fluke or lungworm eggs were detected. There was no difference between EPG in cattle grazing dryland or irrigated pasture. The class of dewormer used was not effective in killing the parasites to the degree expected. Testing of larvae in fecal samples showed that one genus of worm, Cooperia, was most common before and after treatment, followed by the genus Ostertagia. The results show that deworming practices in northern California herds and likely the larger geographic area in the western United States need updating.